Grimsley was a member of the Unova Elite 4 and was addicted to gambling. As an Elite 4 member, he became emo ans sickly after meeting Shauntal and spending too much time in her ghost-infested library.
His prestigious family fell into ruin when his father "accidentally gambled away the family estate" at a drunken party with Colress. He later left Unova traveled to Alola in Pokémon: Hawaii Edition in hopes of winning in a coin flip against The Player so he could take your ass. That is why he added "Uncle" before his name. He appeared frail with sleep deprivation or cancer in his time in Hawaii, and is presumed to have drowned due to his newly discovered "life-purpose" of surfing. He was also known for being a dick to preschoolers at the Battle Tree and being awkwardly hit on by his drunken battle-partner Cynthia.
He was also suspected of being the father of Piers and Marnie, the whitest bitches in all of Pokémon history, so much so that he pretended to be Asian (or, at the very least, embraces Japanese culture) to hide his white guilt.