Thelonius is the henchman of Lord Farquaad and possibly the executioner, as he's the one who tortures Gingy by breaking his legs and dunking him in the milk, as well as threatening the Magic Mirror by suggesting Lord Farquaad to break it. He is also the one who suggests Lord Farquaad choose Fiona, telling him to chose number three while holding up two fingers.
He is seen at Shrek and Fiona's wedding and at Shrek's Karaoke Dance Party where he seems to have become friends with Gingy, his former torture victim.
Thelonius appears at the end sitting in the audience of the movie theater in Far Far Away.
Video Game Appearances
Thelonius appears in Shrek Smash and Crash Racing as one of the eight unlockable racers in this game. Thelonius's kart is the Black Horse and his personal item is a giant stone age axe.
Thelonius appears in Shrek: Fairy Tale Freakdown as an opponent and unlockable champion. His attacks include throwing hand axes, charging at his opponent and punching.
Thelonius isn't really as villainous as he seems. When Fiona and Shrek kiss during her wedding with Lord Farquaad, Thelonius writes "Aawww" on one of the signs used for telling the people on how they should they react.
On Shrek 4-D he kidnaps Fiona and takes her to the raft to kill her, but he is doing it only under the command of Lord Farquaad's Ghost. He accepts Fiona punching him in the face. When she kicks him in the groin, he falls overboard and she apologizes to him. He fell from the waterfall but grabs the branch below it. When Fiona, Shrek and Donkey fall as well, he shows his good side by catching them all in one hand while still holding the branch with his other hand until the branch breaks. When Dragon comes to help them, she takes all of them, including Thelonius.