Bullied by his own parents

Mario's nemesis, Wario, is mercenary, greedy, avaricious, reckless, ruthless, loyal, proud, frank, an adrenaline junkie, athletic, arrogant, and foul-mouthed.

While he always gives the impression of being a violent, rude, narcissistic competitor who disregards rules and fairness... it seems he didn't become that way by chance...