Bruce Banner gets thrown into the DC universe and ends up with a red lantern ring.
Atrocitus sent out the ring to find him someone to be his second in command, but bruce decides that atrocitus is guided too much by his hatred for the guardians and decides to kill atrocitus and take over as leader of the red lantern corps, because he realizes that the corps can be a force for good.
Obviously, this Bruce banner is not canon Bruce Banner from earth 616 or MCU, instead its a slightly more ruthless Bruce Banner, someone not afraid to kill if it's to protect someone.
And he and the hulk are not 2 seperate people, so he's in full control of himself while "hulked out".
Let me know what you think, and if you have some ideas on how to improve the concept.
Also, if you want to use this concept, please send me a message first. Would appreciate it.