TR-4 was a Warforged transmuter who was part of a four-Warforged team who oversaw the Northern Terminus along with some Worker constructs.
In the aftermath of the Ytarran extinction, he and his colleagues began to break down due to lack of repair and eventually MN-8 and CC-1 died of "old age". TR-4 and AB-21, however, were not content to go gentle into that good night and began to cannibalise parts from the other Warforged in order to prolong their own lives. After AB-21 died, TR-4 even managed to find a way to jury-rig incompatible parts, so that he could take from the giant Warforged. However, this greatly reduced his mobility and over time he began to go a little senile.
By the time The Party arrived at the Northern Terminus, TR-4 was growing desperate, as he knew he could not repair his own head. He debated replacing it with the head of one of the other Warforged, in case that would bring them back in his place, but was less than hopeful.
Nonetheless, he continued with his task of defending the Northern Terminus, first trapping The Party in his mobile force wall cube and later, after being convinced of their good intentions, using his transmutation abilities to help them fight off an Orc attack. He kept his spirits up with dark humour, at one point telling The Party that "If you kill me, I'll be very disappointed in you".
He was killed when Delta took over his body in order to avoid dying when the body he had been using (a digging machine) was destroyed. Angel killed him anyway, but it was too late for TR-4.