Timothy Barlow is a member of the band The Ruby and is the drummer (though he "sucks" according to Victor Holloway). He was previously addicted to looking at feet pictures on his phone all day and missed rehearsals. He was helped by Dr. Austerlitz, and then passed the Doctor's details along to bandmate Lily whose fiancé Victor required help.
Eventually, it is revealed that Tim is a full member of the Scarlet Lodge. According to Dr. Austerlitz's notes, he visited Lusst'ghaa in the events of Lust for Darkness and was penetrated repeatedly by the Changed. They would have gangbanged him to death, but he happened to be on a healing platform, so he continually healed his injuries during the gangbang. When he finally escaped, his body had mutated such that it was almost impervious to damage, except for heat. His mind was, however, rather broken, and he became obsessed with his foot fetish, to the point he carries a severed leg around and uses it as a weapon.
Tim is first seen in Lust from Beyond: Scarlet (though the player doesn't know his name at the time). After Alan becomes unable to go to Lusst'ghaa, Dr. Austerlitz, in frustration, orders Tim to go beat Alan. Tim does so with the severed leg, nearly killing him.
Tim is later seen in Lust from Beyond, when Victor is in the Eden Theatre looking for Lily. He stalks him until Victor is captured, after which he drags Victor to his cell. Later, Victor kills his way out of the theatre, and Dr. Austerlitz sends Tim to stop him. Victor defeats Tim despite his superhuman abilities, taking advantage of the steam pipes in the room to exploit Tim's weakness to heat, and kills him.
The first time the player encounters Tim, Victor is searching for the three hands necessary to enter the Hall of Whispers under the Eden Theatre. Tim will enter the downstairs area (where Danny is) and can go to the player's position regardless of where he is. At this stage, the player can escape him by simply running upstairs. Tim cannot be harmed at this stage.
Later, after the player finds the Bone Key, Tim will reappear and this time roam the entirety of the Bloodhouse, which poses a challenge for players who need to traverse the Bloodhouse to find the hands. Again, Tim is invulnerable and goes to the player's location regardless of where the player is or if the player is in stealth. Tim is rather slow, however, so evading him is not difficult.
Finally, when escaping the theatre after returning from the Chamber of Change, Tim appears one last time as a boss fight. Normally, he is invulnerable, as usual, but the room has several steam pipes with small leaking panels. Shooting the panels sends out a temporary blast of steam from the pipe - Tim is weak to heat, so if the steam hits Tim, he will kneel in pain and be vulnerable for a short while. Use this opportunity to shoot him in the head. When he gets back up, kite to another steam pipe and repeat. Note that Tim is still rather slow, but if he gets close to Victor, he will scream and charge, closing the distance with surprising speed.