Irving and Wafflesworth are actually twins; Irving is older by five minutes. Irving was transformed when he was bitten by a radioactive shark.
From an early age, Irving constantly tormented his little brother, probably contributing to Washington leaving home as soon as he could, while Irving stuck around for a few more years.
Still living at home, Irving became a sock smuggler. In the black market, he's regarded as the go-to guy for footwear undergarments of all kinds. Between Chapters V and VI, Nintendoki hired Irving to retrieve Luna's socks, since she would be accompanying Smoosh to the Wafflesworth reunion. However, Luna chose that time to leave Smoosh for parts unknown.
When Irving learned Luna had vanished, he assumed that Nintendoki had set him up, and that Smoosh was actually an undercover police squad there to arrest him. He used a plan he'd spent four years on and kidnapped his mother while framing Washington for it.
Smoosh eventually confronted him and subsequently defeated him in battle.
Irving. Is. A. Douche. Bag. He is as different from his brother as possible: Washington is a gentleman, Irving is a jerk; Washington is intelligent, Irving is brawny. This is possibly why Irving feels the need to torture his brother at every opportunity. However, despite his meanness, he is dearly loved by the rest of his family.
Being a shark, Irving has many shark-like abilities. Foremost of these is his powerful set of teeth, strong enough to easily bite through solid steel. Another potent ability is incredible senses: his smelling is extremely potent, and he even has a sixth sense: the ability to sense a living being's body electricity.