From Bulbapedia, the community-driven Pokémon encyclopedia.

A Cue Ball or Roughneck (Japanese: スキンヘッズ Skinhead) is a type of Pokémon Trainer that first debuted in the Generation I games. They appear as gigantic, hulking bald men. Cue Balls are usually in the vicinity of Bikers. Their Diamond/Pearl appearance has a Gyarados on the back of the vest, much similar to most gangs, indicating they might be thugs of some sort.

They specialize in a combination of Poison-type and Fighting-type Pokémon and are sometimes shown as being affiliated with Team Rocket.

Appearance

Cue Ball Sprites

Image from Pokémon Red and Blue

Image from Pokémon FireRed and LeafGreen

Image from Pokémon Diamond and Pearl

Generation I-introduced trainer classes
Beauty | Biker | Bird Keeper | Black Belt | Boss | Bug Catcher | Burglar | Champion | Channeler | Cooltrainer Cue Ball | Elite Four | Engineer | Fisherman | Gambler | Gentleman | Hiker | Jr. Trainer♂ | Jr. Trainer♀ | Juggler Lass | Leader | PokéManiac | Trainer | Psychic | Rival | Rocker | Rocket | Sailor | Scientist Super Nerd | Swimmer | Tamer | Youngster
Beta classes
Chief | Pokémon Prof.