The connecting record
shownAvengers: Endgame · 2019
Iron Man killed Thanos in Avengers: Endgame.
with a gauntlet he built, and it killed him too
What each of them is ranked on
The killer · Iron Man · rank 17
Tony Stark — comics and screen
He was genetically engineered to pilot a Celestial-killing machine and the machine turned him down — it wanted his brother. So he built his own one, eight reactors of it, and took that into a fight with the Dark Celestials instead. That is the whole character in one anecdote. On screen he takes the six stones off Thanos and uses them, which kills him — Banner had worn the same gauntlet an hour earlier and lived, so this is not a durability feat. It is a nerve feat, and so is the other one.
shownIron Man · 2013
The Aspirants' Godkiller rejects Tony as a pilot; his brother Arno was the intended one.
shownAvengers · vol. 8 #5
Pilots the Godkiller Mk II, of his own construction, against the Dark Celestials. — 2018
shownAvengers: Endgame · 2019
Takes the Infinity Stones into a gauntlet of his own making and uses them, dying of it.
The victim · Thanos · rank 3
The Mad Titan — comics and screen
Everyone cites the Gauntlet. The Gauntlet is his second-best day. Holding the Heart of the Universe he erases all of existence, is talked out of it, and then puts the universe back exactly as it was including the people he had already killed. Then he erases himself, and Adam Warlock is the only one left who remembers any of it happened. The screen version does the smaller, better-told take on the same arc.
shownMarvel Universe: The End · 2003
Wields the Heart of the Universe, erases all existence, then restores it whole.
shownThe Infinity Gauntlet · 1991
Erases half of all living things with a gesture, then defeats Eternity.
shownAvengers: Infinity War · 2018
Completes the Gauntlet and erases half of all life across the universe.
What this does not settle
One death in one work. It is the only place the record puts these two in the same room, and it is evidence about that meeting and nothing wider — not a general matchup, not a rematch, and not a ranking of its own.
The ladder above it is argued from everything either of them has been shown doing; this page is argued from one citation.
Where the two disagree, the disagreement is the point, and it stays visible rather than being resolved by whichever of them happens to be on this page.