Sakumo Hatake is Kakashi's father. We see him very briefly and he is also mentioned briefly. His character wasn't expanded on so there is no point in talking about him. He killed himself because of the shame and ridicule after he went against the rules of the village and abandoned his mission in order to save his comrades. That led to Kakashi believing that those who break the rules of the Ninja world are scum. This was noted during the Kakashi Gaiden arc. His beliefs changed when Obito stood up to him and claimed that while it's true that those who break the rules are scum, but those who abandon their comrades/friends are worse than scum. Sakumo Hatake was also briefly mentioned in Team Kakashi's trip to the Hidden Sand Village, where Chiyo attacked Kakashi, mistaking him for Sakumo, the White Fang of the Leaf. Then he was seen briefly with Kakashi during the pain arc. That was the last we saw of him. His abilities as a Ninja were praised by Minato, and in his time, he was said to be as powerful as the Sannin. His fame overshadowed that of the Sannin and brought fear to his enemies.
Now, let's see how far back this puts us. Kakashi's current age is around 29 - 31 years old. Sakumo died when Kakashi was around 4 - 5 years of age, since he graduated the academy at age 5. All 3 Sannin are around 54 - 55 years old, this would've made them around 27 years old when Sakumo died. This allows us to assume that they had only been dubbed as the Sannin a few years prior to Sakumo's death. Given the time period, we can safely assume that this was before Jiraiya had mastered Sage Mode, before Orochimaru had defected and before Tsunade either learned how to use her Yin seal, or before she had gathered enough Chakra to use it. During this time period, the Sannin would've been above-average. Strong enough to last against Hanzo of the Salamander, but not quite strong enough to win. This puts Sakumo Hatake on their level during this time period. Now, if Jiraiya were still alive, Sakumo would not be nearly as powerful as the present time Sannin.