The oldest and most popular VG character who is STILL having games created after him (thankfully). Made his debut as we know him now (that is, as a plumber) in Mario Bros, alongside his brother Luigi.
However, despite Mario being a plumber, with the release of 1985's Super Mario Bros on the NES things changed. Instead of fixing taps (as he did in the prequel, if you look past obvious technical limitations), he would leap around the television screen, stamping on small brown things and eating mushrooms. Grandparents worldwide were particularly confused by this new phenomenon.
As great a hero as he is, just don't get Mario round if the waterworks go wrong; the bastard won't fix the problem. He is more likely to just jump around and put holes in the fucking ceiling with his head!