Triforians are a race of trifold beings who exist in three different bodies instead of only one. The three different bodies, and their accompanying personalities, are normally joined as one but can be split into three. Once split into three, it can be a very difficult and sometimes painful process to rejoin.
When Trey was separated into three, his forms were of Courage, Wisdom and Heart, although it is by no means guaranteed that it would be the same for all members of that race