Magister Prior Gilhil

Magister Prior Ghilhil is a Plumber who made the rank Magister (an equivalent to a military officer's rank, possibly Colonel; Ghilhil's rank Magister Prior is possibly an equivalent to 'Lieutenant Colonel') and that he is very strict and follows the book closely, since he was even willing to take a Highbreed's word for it that Ben and his team were claiming they were Plumbers, and was even willing to throw Ben, Gwen and Kevin into the Null Void forever.

Ultimate Alien
Magister Ghilhil answered to a distress call aboard Aggregor's ship, only to be told on arrival that it was a computer error. After demanding a search of the ship, he soon locates Aggregor's prisoners, only to be attacked from behind by Aggregor himself as he began reciting the present violation. Aggregor is shown later wearing Ghilhil's uniform, and it is unknown what became of Ghilhil himself. It is possible he may be dead or he's in a cell back on the ship, so this might make Aggregor the 4th alien to murder someone or not, first was Vilgax.

Trivia

 * He's is what similar to what of an Inkursian.