In the comics, Iron Man grew an Infinity Stone inside his brain.

Iron Man is arguably one of the smartest characters in any Marvel Universe, but in the Ultimate Universe,

he accomplished the impossible by growing an Infinity Stone inside his head. In the MCU, Tony Stark's brilliance enabled the Avengers to travel to alternative

timelines and acquire Infinity Stones, allowing them to build their own Infinity Gauntlet and undo Thanos' terrible killing. In various realms, 

Tony Stark obtains Infinity Stones in a variety of ways.In Marvel's alternate Ultimate Universe,

Infinity Stones (or "Infinity Gems" as they're known there) have an entirely different history and purpose than in mainstream comics or the MCU

In the original comics, the Infinity Gems were created by Nemesis, a supreme being from the original reality. In the Marvel Cinematic cosmos,

the Infinity Stones are "singularities" that occurred at the beginning of the cosmos. The Infinity Gems, on the other hand,

are more like white blood cells in the Ultimate cosmos - objects of enormous power that arise in times of great tragedy to help rescue the cosmos from destruction. 

Groot's terrifying new form confirms that he is now a Marvel villain.