Flynn Taggart

Flynn Peter Taggart is an 18 year old drafted into the Space Marine Corps in the mid-21st century. He was sent with the intent to be sent out into deep space with his squad to fight the Strogg, but this was put on hold after the UAC's Mars base put out a distress signal. He decided to hop on this operation, wanting to get some experience for being a Space Marine (his basic training didn't give him any proper training despite going through the paces with two different Drill Sergeants). When they were going to Mars, Flynn was very tired and once they got to Mars, the UAC Facility, he decided to sleep on the garage floor while no-one was looking. While he was doing that, his comrades came under siege by the demons and were completely decimated, leaving Flynn, being the last Space Marine in the hangar.

Personality
Compared to what people expect for the main protagonist in the Doom games, which was represented in Ross' 2013 April Fools Video, Doom Guy's Mind, Flynn Taggart's personality is the complete polar opposite of Doomguy; whereas the Doomguy enjoys killing the demons in creative (and often very messy) ways, Flynn is only concerned in escaping and only engages in combat when faced with no other choice. Flynn has no interest in becoming a marine; his dream job was working as a nature preservationist.

Flynn also mentions food, especially cheese quite often during the early episodes, and has his 21st pet rabbit, named Daisy. He talks about them quite often in the series. He's also makes theories that sound crazy to people who don't follow his thought process, which comes off annoying since he won't shut up.

Flynn has dysnomia, a mild form of anomic aphasia (a condition that affects the speech centers of the brain), which he sustained after receiving a head injury in middle school when someone roundhouse-kicked him. The condition starts to heal following his "blue balling" by the Soul Sphere, which also increases his metabolism and physical healing factor.

Erin
She was an acquaintance of Flynn's that he met on the SMC Carrier/Destroyer. He mentions she was a vehicle maintenance and repair technician.

Winston
Flynn became friends with Winston during his time in Boot Camp, as he was the only one that understood his situation during the time fighting the Strogg. His friend also knows about sign languages, which Flynn wishes he can adapt before they go their separate ways.

Uncle Stan Blazkowicz
Flynn was very close to his uncle and often spent his weekends meeting him at the gun range, which is where most of his experience with guns and fast reloads comes from.

Crash
Crash was Flynn's first of two Drill Instructors during his time in the Marines, and in his opinion the lesser of the two. By his own account Crash did a poor job at molding him (and presumably his fellow cadets) to meet military standard and left him, in his own words with 'the mindset of scared kittens' in combat situations. He was initially resentful towards her over this fact, however he later regretted this when he discovered that her apparent incompetence was due to her suffering domestic abuse, and resolved to make amends however he could if he saw her again.

Craig
Flynn passed Craig's corpse on the second floor, surrounded by Imps, though he only learned this later. Flynn was under the impression Craig was, in his own words, "a prick" because of his affair with Crash during the breakdown of her marriage.

Dimitri Paramo
During Flynn's exploration, he happened to find Dimitri hiding in a corner, with his dead friend Tommy lying in the center of the room. They travelled together for a few rooms in the hope of reaching the command center, during which time they exchanged much banter, with Dimitri calling Flynn out on his near-constant commentary and his outlandish theories to explain the creatures, and Flynn criticizing his brash attitude to engaging the enemy. This did not last, however, and Flynn accidentally shot Dimitri dead while trying to aim and fire a minigun.

The Alternate Flynn Taggart
In Episode 6.5, Flynn encounters another version of himself from a different universe (implied to be the version of Flynn Taggart featured in the Doom novels), who he describes as having a 'handsome' sounding voice. He finds the differences between their universes perplexing: for example, Alien had multiple alternate sequels where Ripley, Hicks and Newt survive, but Terminator never had a sequel; in its place however, low-budget rip-off R.O.T.O.R. did, which leads to a tangent where Flynn vows to make his other self watch through Terminator 2: Judgment Day. The alternative Flynn tries to explain the situation but is cut off and pulled back to his own universe before he can fully explain why he came, but he does mention that the demon invasion is happening across many other worlds and that the Flynn of Taggart's Journey was the very last Flynn on their list of Flynn's to recruit to repel the invasion force.