The eldest and most Loyal Son of Kaizen Rhoisoh . He might not be the first born but he's at least a couple of hundred years old. He was born on Rhoisoh before the exodus to Moonlight Oasis, and did not go into hiding when his father pretended to be dead. being a shape shifter he could easily travel disguised as someone else. he can even mimic their genetics in the transport codes in the same way Sen'tran hides jason and Jonathan and Desmond's Genetics.
In Jason's time he is seeking revenge on Sen'tran and various others for the death of his father who was killed by Darcy with the help of Rain and Sen'tran
Thearon is a shape shifter with psychic power and he therefor has no dreaming ability [shifter/telepaths can't have dream skills. therefor it is probably his dream skills which prevented Jonathan form developing shifting skills]
He thinks he ought to be Paragan in the reunited Empire because His father was [he believes unfairly] excommunicated from the Paragan line. By Sen'tran.
his basic for is a wildcat, so the battle with him in the form of a wildcat evokes Jason's other battle to protect Harris from the wildcat, and Jason seeing Harris as a wildcat when they first meet foreshadow that.
Thereon is a half-brother to Jonathan and Darcy, having the same father but not the same mother. his mother was Rhoisohan.