Marvel: Contest of Champions is a widely multiplayer game set in the Marvel TM Universe.
Story
The Collector, an Elder of the Universe, obtaining the Isosphere, teams up with Kang the Conqueror to
capture every hero, villain, and rogue, and use them as pawns in a greater game. In the game, you are called a summoner.
Kang: "Collector!!! Enough with the flashback! You promised a worthy opponent for this contest!...The legendary Isosphere! Can I hold..."-Collector: "Patience, my blue friend! It isn't yours...yet...See? Your opponent arrives...lets begin!...Welcome Summoner! You have been chosen to represent Earth in a cosmic contest of champions against Kang the Conqueror. I am the Collector, the organizer of this contest. The stakes are simple: win and be granted untold power. Lose and you shall be put in my collection... permanently!"
You (the player) defeat Kang, and you then reign against Thanos. After many tries, you finally manage to defeat Thanos in his quest for ultimate power. A new character, who is the real director of the contest, appears in the story. After you defeat Kang, the Collector finally tells you the character's name: the Maestro. Now, you and your ally, the Collector, venture to stop the Maestro in his quest for ultimate ISO-8 power.
The Maestro then obtains extremely precious ISO dust, and the Collector asks him to give it back. The Maestro says he has been "saturating the Collector's champions with ISO-8 and incubating it in their bodies as they battled in the arena until their pure essence could be extracted". The Maestro fused the ISO dust into its final form. He then defeats the Collector.
Collector: "NO! I MADE A TERRIBLE MISTAKE! ARGHHH!"
The Maestro then resumes his quest for ultimate power (yeah, he's really an extremely evil megalomaniac). But not so fast, Maestro!
Maestro: "Now, once my full power returns, I can resume my--"
Thanos punches him in his face! But…who let HIM out of his crystal?! GUILLOTINE!!
Thanos: "Don't be afraid, curse-bearer. You did the right thing, releasing me from my crystal. Hmm. I have never seen a gem quite like you before. Newborn. Unnamed. Pure."
Thanos places the ISO gem into his gauntlet (yep, you guessed…the INFINITY GAUNTLET).
Thanos: "Hush now…let Thanos of Titan introduce you to the universe. You are an infinity stone…and all this shall be yours one day."