The Grandmaster is one of the oldest living beings in the universe. He and his brothers (one of which is the Collector) don't even remember their beginninsg because they're that old. They are practically immortal, and super powerful, but Grandmaster doesn't use that power for anything except getting really good at games. For real. His thing is to learn how to master every game and come up with new games. That's like Rob Kardashian using all that wealth to make socks. It's a waste.
The craziest game he ever played was against Death. After his the Collector was killed, Grandmaster wanted to bring him back, so he played a game against Death (just like in Bill and Ted's Excellent Adventure). He ended up winning, but then Death pulled the bitch move of saying, "OK, but you have to die to bring him back." Grandmaster did it and ended up saving Collector's life.