The Mark XLII (Mark 42), known by its code name Extremis or the “Prodigal Son” is an Autonomous Prehensile Propulsion Suit Prototype was the forty second armor, as well as one of the many newly built suits, created by Tony Stark sometime after the events of The Avengers. It served as a prototype for Mark - XLIII which could be found in Avengers : Age Of Ultron.

It was the armor featured in the movie Iron Man 3, and made its debut in the movie during the start, when Tony creates it in his basement, and tests the suit's functionalities. It was seen throughout the whole movie as Tony's main suit, and it was later destroyed by self-destruction when Tony ordered J.A.R.V.I.S. to do so, after remotely controlling it to trap Aldrich Killian within it to blow him up and finish him for good.

The suit is well known for its special ability to fly in separate pieces and wrap itself around Tony's body, piece by piece through 49 state-of-the-art computer chips that was implanted in his arms called Micro-Repeaters, which enables him to communicate with his armor.