Trok'larr was a P'tarr. One day as he ambled down a path, he encountered the Fourth Doctor and Leela. The Doctor tried to communicate with him, but he ran off, towards a certain tree. After he ate the bark of the tree, he started talking to them in a strange language. Because Leela had eaten fruit from a different tree, she could understand him and acted as interpreter for him and the Doctor.
The group was attacked by partially Cyber-converted humans, and though they had been ordered not to kill, Trok'larr was killed by Abel. (PROSE: One Bad Apple)