King

is a giant gorilla that lives on the island Killer B and A train at. B calls him, as a sign of affection.

Confining the Jinchūriki Arc
King appeared before the Kumo and Konoha ninja when Motoi guides them through the island. As King was about to attack them, Killer B calms him down telling him they're with him and they greet each other by bumping fists. King is later seen with Kintoki and the other bears, watching with interest as Guy opened his Eight Gates.

Trivia

 * King's name is likely based on King Kong's.