Loeb's seems to be a man on the side of justice who was attacked and nearly killed in the line of duty by a strange parasite wrapped around his heart. Events turned when he and his wife Samantha Loeb exchanged information about "Little Hill", revealing that everything was a sham. ("In Which We Meet Mr. Jones")
He was revealed to be working with Joanne Ostler, where they used the Equation in conjunction with a device to reach through solid matter. He then killed Ostler after they confirmed the experiment worked. ("The Equation")
He used the technology acquired to break into bank vaults, stealing only a single safe deposit box each time. After Loeb and his team gathered four of the safe deposit boxes, they went to Little Hill Field and constructed a strange, ring-shaped device. After triangulating certain coordinates, they successfully teleported David Robert Jones from his prison cell in Frankfurt, Germany to Little Hill. ("Safe")
After kidnapped Olivia Dunham and performing tests on her, he killed Dr. Miles Kinberg and Dr. Russell Simon with a Mutated cold virus. After Olivia escaped she discovered his duplicity and went to his house to find evidence. While there Samantha Loeb tried to kill her and Olivia was forced to kill her. Mitchell was then arrested. ("Bound")
- The Fringe website refers to this role as MITCHEL Loeb in the Safe episode recap. In his first two appearances, the recap referred to the character as MITCHELL.
- Loeb is called Captain, which fits in with the fact that the heist team he directs in Safe are all former military officers.
- Loeb's name is a play on Michelob, a brand of pale lager by Anheuser-Busch.
"A word of advice... don't pry into things you couldn't possibly understand."
- - Loeb to a prying team member. (Safe)