The first King, the Silver King.
Adolf K. Weismann (Adorufu Kā Vaisuman) was the Silver King, formerly a researcher in Germany who experimented with the effects of the Dresden Slate. He was ejected from his original body by the Colorless King and had since inhabited the body of a teenage boy, where after becoming amnesiac, Weismann assumed a new identity, Yashiro Isana.

(Source: K-Project Wikia)