Why Did Tony Stark Have to Use the Infinity Stones? In "Avengers: Endgame," Tony Stark (Iron Man) used the Infinity Stones as part of the plan to defeat Thanos and his army. This decision was made for several reasons: Desperation: The Avengers were facing a seemingly unbeatable foe in Thanos, who had the Infinity Gauntlet and had already used it to devastating effect. With the fate of the entire universe hanging in the balance, the Avengers had no other viable option [...]