Master Finn is RJ's father and bearer of the Shark Animal Spirit.
Master Finn trains Casey the ways of the shark in the form of Shark Sabers. However, he tried unsuccessfully to teach his style to R.J., causing a rift between them that is not mended until R.J. proves his strength by demonstrating his own control over the Wolf Spirit. Master Finn trains Casey to use his Shark Sabers and teaches him how to channel his Animal Spirit. Later, he is captured by the Phantom Beasts along with the other masters and his animal spirit is transformed into the Shark Ranger. He becomes trapped in one of the Crystal Eyes when his Spirit Ranger is destroyed in battle with the Rangers. Flit saves the Crystal Eye from being thrown in the sea and gives it to R.J., who frees his father. The Shark Ranger now fights along with the other Rangers when summoned by either Casey or Master Finn. He returns later on with the other masters to test the rangers if they can earn their Order of the Claw master status. However, he fails Casey. By the end of the series, he took part in the final battle and like his fellow Masters, reached the highest level of his animal spirit in order to defeat Dai Shi's forces. He was present when Dai Shi was destroyed.