Slowking are Slowpoke who were bitten on the head by a Shellder. This is often the result of a Slowpoke holding a King's Rock because a Slowpoke holding this item will attract Shellder to bite its head, rather than its tail. The resulting poison that the Shellder secretes reaches Slowpoke's brain, causing it to become extremely intelligent. Upon evolving, the lighter-coloration on the tip of Slowpoke's tail disappears, and, like Slowbro, Slowking has a scaled underbelly.

In appearance, Slowking looks much like a bipedal Slowpoke with its Shellder resembling a crown, although the shape of Slowking's eyes and the scales on its belly cause it to differ from its pre-evolution. There is a small red gem on the upper part of the "crown." Slowking also somehow gains a red and white ruff around its neck to emphasise its "regality."