Marcus is an NPC in Borderlands 2
He has missions for you and can also sell you gear
There are two things you should know about Marcus Kincaid, the foremost arms dealer on Pandora. Firstly: you can always trust him to sell you quality firearms. Secondly: you cannot trust him in literally any other context. Marcus cares about profit, and profit alone—so long as you intend to keep killing people and buying stuff, the two of you will be thick as thieves.