It's Mario and Luigi from the hit game series Mario and Luigi! Funnily enough, it's been like 4 years since the last time I made Mario fan art that actually has Mario in it.
I have been playing through Brothership, and I'm having a lot of fun with it. Yeah, it has some pacing issues, and it took some time to get used to the different controls, but other than that it really seamlessly picked up where the series left off.