Kabuto used Impure World Resurrection to resurrect the fallen Akatsuki members for Madara. He then resurrected another person, whose face we don't see. We do, however, see Madara taken aback by this person, impressed with Kabuto.
I predict that Kabuto resurrected Madara's dead brother, Izuna. It makes sense for Kabuto to do this, and it makes sense for Madara to react in the way that he did.
I would have first thought that Kabuto resurrected Shodaime, but the third Hokage already sealed Shodaime in the belly of the death god during his battle with Orochimaru.
I predict that Kabuto resurrected Madara's dead brother, Izuna. It makes sense for Kabuto to do this, and it makes sense for Madara to react in the way that he did.
I would have first thought that Kabuto resurrected Shodaime, but the third Hokage already sealed Shodaime in the belly of the death god during his battle with Orochimaru.