In the book
A huge mountain lion bigger than Kingdok who views himself as neutral in the conflict between the humans and the Lord of the Locusts despite lopsided affiliations. He is the guardian of the Eastern Border. His personal views are that there is no such thing as "good" and "evil", only that power matters above all and that friendship and love is meaningless. He despises both Dragons and Rat Creatures but works for the Hooded One in exchange for land and spoils of war. His name is mispronounced as 'Rock Jaw' by the Bone cousins.
In the narrative, Roque Ja repeatedly emphasizes the need to take sides as he takes Fone Bone, Smiley, and their animal allies prisoner to trade off to Kingdok. They briefly escape him during a conflict with the Rat Creatures, but Roque Ja pursues and captures them once more. When approached by Kingdok, however, Roque Ja is attacked by the monster, giving Fone and the others a chance to escape. In the process, he rips out Kingdok's tongue and keeps it as a bizarre trophy.
Despite making a deal with The Hooded One for the capture of Thorn and Phoney Bone, Roque Ja never succeeds or really enacts on this deal. It is presumed that he is back on his mountain range, residing as usual.