Wario is one of the seven star children and an adventurer and treasure hunter. He is also the founder and CEO of WarioWare Inc. Wario was Mario’s rival, but has since buried the hatchet with him. (Add source to that microgame)
Yoshi’s Island DS
Super Mario Land 2: 6 Golden Coins
While Mario was away in Sarasaland, Wario took over his castle and made it his own.
Mario and Wario have known each other since they were babies.