Chairman of the UAC, Head of the UAC Mars, Project Director of the Argent Facility
Samuel Hayden was born to the powerful Hayden family and was a very prodigious intellectual and philanthropist. After he was appointed as General Director of the Global Science Council, the UAC recruited him. Soon after Argent energy was discovered on Mars, Hayden subsequently took over the leadership of the UAC.
Soon after the Argent Tower was constructed in 2127, Hayden was diagnosed with an incurable brain cancer and left with a few months to live. Hayden avoided his death by transferring parts of his brain into a 3-meter tall mechanical body. It was implied that Hayden chose this form for his expeditions into Hell.
Hayden led the first manned expedition into Hell in 2145 in which he discovered the Doom Slayer, simply called "Doom Marine". He had the Marine recovered and kept him personally under his watch away from the auspices of his disgruntled colleague Olivia Pierce. Hayden's relationship with Pierce gradually deteriorated due to her deranged, religious obsession with Hell which ultimately corrupted her.
After Pierce betrayed Hayden and planned to open the gates of Hell, Hayden awakened the Doom Marine and tried to persuade him of assisting him in stopping Pierce. He is harshly rebuffed twice at the beginning of the game, though Hayden claims to be willing to accept full responsibility for Hell's invasion.
After the Doom Marine killed Pierce and stopped Hell's invasion, Hayden betrays the Doom Marine, taking the "Crucible" artifact from him to continue exploiting Hell's resources for the sake of humanity's progress before sending the Doom Marine to an unspecified location. Before he does so however, Hayden states his certainty that he and the Doom Marine would meet again.
- Despite having been diagnosed with "incurable brain cancer", Samuel Hayden had his frontal and temporal lobes transferred to his new body. It is possible that these parts of his brain were free of cancer, and that he chose to replace his whole body rather than simply replace the cancerous parts of his brain with cybernetic equivalents.
- Hayden's original human form can be seen in a hallway showing various scientists.
- He is literally immortal from aging since his body is constantly maintained by stem cell and neuro-maintaining agent, however, he is not immune from being killed.
- Due to his cybernetic body Samuel Hayden is over 130 years old.
- S. Hayden has a phonetic similarity to "Satan", which may indicate Samuel Hayden may be revealed to have connections to Hell too in some way.
- He often activates the restraining chip, which he installed inside the Doom Marine's armor. He starts activating after they first meet face-to-face to prevent the Doom Marine from attacking him.