Which champion’s ultimate can revive an ally after death? Zilean’s ultimate, Chronoshift, can.
Zilean’s Chronoshift can place a protective time-bomb-like effect on an allied champion. If that champion takes fatal damage while the effect is active, they enter a brief resurrection state instead of remaining dead, then return to life with a portion of their health restored. The spell can be cast on Zilean himself or on an ally, making it useful for protecting a carry, saving a frontline engager, or changing the outcome of a team fight.
The ability reflects Zilean’s time-manipulation theme. His other spells let him place time bombs, accelerate allies, and slow enemies, while Chronoshift represents rewriting a champion’s immediate fate. Timing matters: casting it too early can let enemies wait, while casting it too late may fail to protect the target.
The distractors do not provide the same standard ally-resurrection ultimate. Tahm Kench can rescue and transport an ally, Karthus continues acting briefly after death through his passive, and Soraka heals allies with her ultimate. None of those effects is an ally revival, making Zilean the canonical answer.