Trefaji is one of the gorilla jail guards in Marim, along with his comrade Aberab.
If he sees players in their human form outside of the cell or within one space of the cell wall, he will deal some damage (normally around 100 life points, but potentially up to 200), and send them back in.
When the player is in gorilla form, he can be blocked, so he would 'teleport' around the player. This could be useful for questers who wish to save time and food by simply waiting for the guard to go north of the player in monkey form and quickly follow the player so the guard would 'teleport' around, running through the player and avoiding being jailed again.
Sometimes, when attempting to block Trefaji or Aberab as described above, a glitch can occur where both guards patrol the jail at the same time. This has not been fixed.