1st
Hashirama has been noted by both Madara Uchiha and several Konoha Jonin to be regarded as the most feared ninja of his time. He was said to be one of or perhaps the most powerful of ninjas during the ninja wars, and the only person who was capable of matching him and his clan was Madara and his Uchiha clan. He was greatly respected by all and even Madara had respect for his strength.
Proof of how undoubtedly an extremely a formidable ninja he was is shown by him defeating both Madara and the Nine-Tailed Demon Fox (who was under Madara's control at the time). This is remarkable since Madara is a wielder of the Eternal Mangekyo Sharingan, an advanced form of the Mangekyo Sharingan. Defeating the demon fox alone would be a legendary feat, as the Fourth Hokage had to literally give up his life to seal the demon fox. He also defeated the powerful Akatsuki member Kakuzu at some point. During his resurrected corpse's battle with Hiruzen he is shown to be a considerable hand to hand combatant and could use powerful Genjutsu. Flashbacks to his battle with Madara show he also had some summoning prowess, conjuring various weapons via scrolls.
He was most famous for his Wood Release jutsu, an ability to mix earth and water natured chakra to create a new element: wood. By converting chakra into source of life, he was able to create trees and cause them to grow to great sizes and diverse shapes at will. This ability was apparently unique to him, since his neither his brother Tobirama nor granddaughter Tsunade did not inherit this talent despite their own imressive talents for chakra control, and Yamato only acquired it (albeit much weaker in raw power) through genetic manipulation by Orochimaru. Yamato has also shown great skill in standard water and earth techniques so it is presumed Hashirama could as well.
The ability Orochimaru most highly praised him for, however, was his unique ability to control the Tailed Beasts bending them to his own will, and suppressing their chakra. Madara also mentions that at one time he had several tailed beast under his control and later dealt them out to the other great Hidden villages in order to equalize the balance of power. It would seem this ability is greatly amplified by his very valuable necklace composed of a shard of crystalline chakra, though how this works is unknown.
Also, the famous Scroll of Sealing that was made by Hashirama himself heavily implies that he too know a vast number of jutsu not like the Third Hokage.
2nd
He was hailed for being the greatest master of Water Release jutsu, being able to create water from nothing, allowing him to use any water jutsu without requiring a water source. However, it has been speculated that he was just gathering the water vapor in the air to fuel his all powerful jutsus. It must be noted that even if this was the case the sheer quantity of water needed would necessitate gathering moisture from a very large area. Such a feat would be just as impressive as creating water from nothing.
Beyond his formidable ability to create (or gather) water his prodigious skill with water jutsu also extended to cutting out a significant portion of the hand seals used to mold a jutsu. For example the Water Release: Water Dragon Blast Technique usually requires the largest amount of hand seals ever seen in the Naruto Universe, 44 hand seals, however he is shown to only require two hand seals.
Also, during his fight against Hiruzen, in the anime only, he displays great abilities in manipulating water, such as using it for projectiles, or tentacles to drag the opponent down in the water. He also displayed tremendous taijutsu and genjutsu prowess.
In an anime filler arc, it was said that he wielded the Sword of the Thunder God (雷神の剣, Raijin no Ken)), a blade with electrical abilities.
3rd
Hiruzen was called "The God of all Shinobi" and The Professor (プロフェッサー, Purofessā) due to his mastery in all forms of shinobi combat and his vast knowledge of jutsu, purportedly knowing all the jutsu within Konoha. Hiruzen may well be "The Most Intelligent Shinobi in Ninja History". The first jutsu he is seen using is the Telescope Technique which allows him to observe others through his crystal ball over long distances. With Roof Tile Shuriken, he can launch nearby tiles at an opponent with varying intensities, and by throwing a single shuriken at an opponent he can replicate it to surround the opponent through Shuriken Shadow Clone Technique. This shows that Hiruzen is adapted to every battleground in Konoha and is able to use his surroundings to his advantage.
The more battle-oriented jutsu he is seen using primarily consist of elemental attacks, specifically attacks dealing with fire and earth. Fire Release: Fire Dragon Flame Missile allows him to exhale a stream of fire from his mouth. Earth Release: Earth Flow River creates a river of mud beneath the opponent to throw them off balance, and he can use the mud with Earth Release: Earth Dragon Bullet, which creates a dragon's head that launches mud balls at an opponent. He has also shown to be adept in elemental jutsu combo attacks as seen when he ignites the mud ball projectiles with Fire Release: Fire Dragon Missile. Earth Release: Earth Style Wall allows Hiruzen to spit a stream of mud that solidifies into a protective shield.
Hiruzen also has a personal summon: Enma, the Monkey King. Enma can turn into a diamond-hard staff which can alter its length and width at will. This staff is Hiruzen's weapon of choice, and he shows great proficiency in wielding it.
Hiruzen is unarguably one of most powerful shinobi in Shinobi History. He has even been called by the most powerful Hokage in history. Enma commented on his battle with Orochimaru that it was "miserable" compared to Hiruzen's prime even though Hiruzen had clearly been able to withstand Orochimaru, Hashirama (first Hokage) and Tobirama (second Hokage), even to the extent of repelling and withstanding Hashirama's Wood Release and Tobirama's Water Release techniques and able to blow up both Hashirama and Tobirama's arms and legs respectively. He is also the longest living and longest reigning Hokage, having defeated all foes that came before him (that is until old age took its toll).
4th
Minato's brilliance became evident from creating several distinctive techniques, including the Flying Thunder God Technique, which essentially allowed him to teleport to any location with the use of a special seal. He also created the Rasengan, a technique that does not rely on hand signs, but instead uses a concentration of spinning chakra in the palm that causes immense damage to its target on contact. Later in the series it is revealed that this signature technique is actually incomplete. Minato had planned to add his own nature manipulation training to the Rasengan, making it even more powerful, but couldn't manage to combine the two prior to his premature death. Minato's possibly last technique was the Dead Demon Consuming Seal, which was used to seal the demon fox into Naruto, at the cost of his own life.
It is unknown exactly how strong Minato was in combat, but he is considered by many as quite possibly the most skilled ninja the Leaf Village has ever produced. He was undoubtedly extremely powerful, as enemy nations considered fighting him certain death for the ninja sent against him, leading to a flee-on-sight order he is regarded as the greatest shinobi the Leaf Village ever produced. He earned the nickname Konoha's Yellow Flash from his unrivaled sheer speed. Once, during the Third Great Shinobi War, he was able to defeat 50 enemies just by directing his kunai with the special seals on them. It seems to be that he kept teleporting around the terrain because, he was able to defeat them all shortly and without a scratch.
Hashirama has been noted by both Madara Uchiha and several Konoha Jonin to be regarded as the most feared ninja of his time. He was said to be one of or perhaps the most powerful of ninjas during the ninja wars, and the only person who was capable of matching him and his clan was Madara and his Uchiha clan. He was greatly respected by all and even Madara had respect for his strength.
Proof of how undoubtedly an extremely a formidable ninja he was is shown by him defeating both Madara and the Nine-Tailed Demon Fox (who was under Madara's control at the time). This is remarkable since Madara is a wielder of the Eternal Mangekyo Sharingan, an advanced form of the Mangekyo Sharingan. Defeating the demon fox alone would be a legendary feat, as the Fourth Hokage had to literally give up his life to seal the demon fox. He also defeated the powerful Akatsuki member Kakuzu at some point. During his resurrected corpse's battle with Hiruzen he is shown to be a considerable hand to hand combatant and could use powerful Genjutsu. Flashbacks to his battle with Madara show he also had some summoning prowess, conjuring various weapons via scrolls.
He was most famous for his Wood Release jutsu, an ability to mix earth and water natured chakra to create a new element: wood. By converting chakra into source of life, he was able to create trees and cause them to grow to great sizes and diverse shapes at will. This ability was apparently unique to him, since his neither his brother Tobirama nor granddaughter Tsunade did not inherit this talent despite their own imressive talents for chakra control, and Yamato only acquired it (albeit much weaker in raw power) through genetic manipulation by Orochimaru. Yamato has also shown great skill in standard water and earth techniques so it is presumed Hashirama could as well.
The ability Orochimaru most highly praised him for, however, was his unique ability to control the Tailed Beasts bending them to his own will, and suppressing their chakra. Madara also mentions that at one time he had several tailed beast under his control and later dealt them out to the other great Hidden villages in order to equalize the balance of power. It would seem this ability is greatly amplified by his very valuable necklace composed of a shard of crystalline chakra, though how this works is unknown.
Also, the famous Scroll of Sealing that was made by Hashirama himself heavily implies that he too know a vast number of jutsu not like the Third Hokage.
2nd
He was hailed for being the greatest master of Water Release jutsu, being able to create water from nothing, allowing him to use any water jutsu without requiring a water source. However, it has been speculated that he was just gathering the water vapor in the air to fuel his all powerful jutsus. It must be noted that even if this was the case the sheer quantity of water needed would necessitate gathering moisture from a very large area. Such a feat would be just as impressive as creating water from nothing.
Beyond his formidable ability to create (or gather) water his prodigious skill with water jutsu also extended to cutting out a significant portion of the hand seals used to mold a jutsu. For example the Water Release: Water Dragon Blast Technique usually requires the largest amount of hand seals ever seen in the Naruto Universe, 44 hand seals, however he is shown to only require two hand seals.
Also, during his fight against Hiruzen, in the anime only, he displays great abilities in manipulating water, such as using it for projectiles, or tentacles to drag the opponent down in the water. He also displayed tremendous taijutsu and genjutsu prowess.
In an anime filler arc, it was said that he wielded the Sword of the Thunder God (雷神の剣, Raijin no Ken)), a blade with electrical abilities.
3rd
Hiruzen was called "The God of all Shinobi" and The Professor (プロフェッサー, Purofessā) due to his mastery in all forms of shinobi combat and his vast knowledge of jutsu, purportedly knowing all the jutsu within Konoha. Hiruzen may well be "The Most Intelligent Shinobi in Ninja History". The first jutsu he is seen using is the Telescope Technique which allows him to observe others through his crystal ball over long distances. With Roof Tile Shuriken, he can launch nearby tiles at an opponent with varying intensities, and by throwing a single shuriken at an opponent he can replicate it to surround the opponent through Shuriken Shadow Clone Technique. This shows that Hiruzen is adapted to every battleground in Konoha and is able to use his surroundings to his advantage.
The more battle-oriented jutsu he is seen using primarily consist of elemental attacks, specifically attacks dealing with fire and earth. Fire Release: Fire Dragon Flame Missile allows him to exhale a stream of fire from his mouth. Earth Release: Earth Flow River creates a river of mud beneath the opponent to throw them off balance, and he can use the mud with Earth Release: Earth Dragon Bullet, which creates a dragon's head that launches mud balls at an opponent. He has also shown to be adept in elemental jutsu combo attacks as seen when he ignites the mud ball projectiles with Fire Release: Fire Dragon Missile. Earth Release: Earth Style Wall allows Hiruzen to spit a stream of mud that solidifies into a protective shield.
Hiruzen also has a personal summon: Enma, the Monkey King. Enma can turn into a diamond-hard staff which can alter its length and width at will. This staff is Hiruzen's weapon of choice, and he shows great proficiency in wielding it.
Hiruzen is unarguably one of most powerful shinobi in Shinobi History. He has even been called by the most powerful Hokage in history. Enma commented on his battle with Orochimaru that it was "miserable" compared to Hiruzen's prime even though Hiruzen had clearly been able to withstand Orochimaru, Hashirama (first Hokage) and Tobirama (second Hokage), even to the extent of repelling and withstanding Hashirama's Wood Release and Tobirama's Water Release techniques and able to blow up both Hashirama and Tobirama's arms and legs respectively. He is also the longest living and longest reigning Hokage, having defeated all foes that came before him (that is until old age took its toll).
4th
Minato's brilliance became evident from creating several distinctive techniques, including the Flying Thunder God Technique, which essentially allowed him to teleport to any location with the use of a special seal. He also created the Rasengan, a technique that does not rely on hand signs, but instead uses a concentration of spinning chakra in the palm that causes immense damage to its target on contact. Later in the series it is revealed that this signature technique is actually incomplete. Minato had planned to add his own nature manipulation training to the Rasengan, making it even more powerful, but couldn't manage to combine the two prior to his premature death. Minato's possibly last technique was the Dead Demon Consuming Seal, which was used to seal the demon fox into Naruto, at the cost of his own life.
It is unknown exactly how strong Minato was in combat, but he is considered by many as quite possibly the most skilled ninja the Leaf Village has ever produced. He was undoubtedly extremely powerful, as enemy nations considered fighting him certain death for the ninja sent against him, leading to a flee-on-sight order he is regarded as the greatest shinobi the Leaf Village ever produced. He earned the nickname Konoha's Yellow Flash from his unrivaled sheer speed. Once, during the Third Great Shinobi War, he was able to defeat 50 enemies just by directing his kunai with the special seals on them. It seems to be that he kept teleporting around the terrain because, he was able to defeat them all shortly and without a scratch.