A bored billionaire with a genius level IQ, Mr Terrific decided to try to find something that would challenge him.  Nothing worked until he became a vigilante and used gadjets and stratagy to fight criminals.   This brought him to the attention of the Justice League, where he became Coordinator Of Resources, meaning he decides where everyone gets deployed.   He replaced the Martian Manhunter, who went on sabbatical to "find himself".
He loves it.