I agree with angel that he's a wolf or a coyote. Coyote because they are the tricksters of Native American culture and are also wise father figures. I almost said a Tanuki because they are a playful shapeshifter in Japan but they have this sexual element that doesn't quite jive with RJ. I definately think RJ is a shapeshifter thou, based on his surfer affectation and his secretive nature (and also because I know what's going to happen later in the series with his character <.< >.>). He could possibly be a fox/kitsune.
I think I'd go coyote or fox too. Hedging my bets though, since I also said something about cats to angel above. ;)
Just based on what (admittedly little) I know about fox/coyote lore, I'd probably edge out fox just above coyote. They've got that beautifully innocent expression - just before they trick a chicken into offering its neck for supper.