|Killzone: Shadow Fall|
- "I've always tried to protect you, son. I'm sorry I couldn't be that person."
- —Thomas Sinclair[src]
A highly decorated Shadow Marshal of the Second Extrasolar War, Thomas Sinclair was active in numerous operations that were instrumental in securing the ISA's victory. He was involved in the formation of the Vektan Security Agency and was mostly likely responsible for the instigation of violence and unrest to create a perceived Helghast threat. He moved through the ranks of the VSA to become agency head within a few years.
Many questioned this rapid rise; some claimed Sinclair used information gathered from his ties to the intelligence community as blackmail. He is a staunch patriot and idealist. This personal view is a major factor in his decision making process against Helghan.
On December 27, 2370, Sinclair helped Michael Kellan and his son Lucas to escape from New Helghan. Unfortunately, Sinclair was only able to save Lucas, as Michael was killed by Helghast soldiers. Sinclair fathered Lucas and, within over two decades, eventually becoming Lucas' mentor and father figure, and later his superior in the Shadow Marshals.
Twenty years later, in 2390, when rising tension between the Vektans and Helghans came close to war, Sinclair sent Lucas to infiltrate New Helghan and recovering classified data relating to an ISA bio-tech weapon experiment, headed by Dr. Hillary Massar, developed on the ISC Cassandra to be used as a deterrent against the Helghast. Sinclair ordered Lucas to scuttle the Cassandra to prevent the experiment from falling into Helghast hands. However, Massar willingly defected to the Helghast and allowed her bio-weapons research to be used against the Vektans. Sinclair placed a high priority on Massar's capture.
Following an attack on the VSA headquarters by the Black Hand under their leader Vladko Tyran, Sinclair dispatched Lucas to again infiltrate New Helghan and locate Tyran. However, Lucas was recaptured and tortured by the Helghast, but soon returned to the VSA and informed Sinclair of Chancellor Hera Visari's alliance with Jorhan Stahl and their intentions to ignite another war with Dr. Massar's bio-weapon. Sinclair, however, was very displeased to hear Lucas had decided to side with Visari's daughter Echo on calling for the VSA to stand down from further provoking war with New Helghan.
Refusing to consider Lucas' words, Sinclair had Lucas sent to Helghan, where Massar had finished preparing her bio-weapon, to take custody of Massar. However, after Lucas and the ISA fought off waves of Helghast soldiers, Echo appeared, and held Massar and an ISA agent at gunpoint. Sinclair overhears the heated confrontation, and angrily orders Lucas to kill Echo. Lucas did not follow Sinclair's orders however, and during a moment of hesitation, allowed Echo to kill Massar and the ISA agent, causing Sinclair to brand the Shadow Marshal a traitor. Despite trying to be reasoned by Lucas in allowing Massar to be killed, Sinclair condemned Lucas's disobedience, questioned his audacity in allowing Massar to be killed, and stated that if he sided with Echo, he couldn't guarantee his safety.
With Lucas having gone rogue, Sinclair soon commanded the ISA into launching an assault on Jorhan Stahl's base on Helghan. He was then contacted by Lucas into aborting the assault as Stahl was about to activate Massar's weapon, but refused to listen, stating that while Lucas may have lost what matters as a soldier, he hasn't. Also, despite Lucas's final warnings, telling him that Stahl has the weapon and that he can get to him and stop the weapon from firing, and that he's simply walking into a trap, Sinclair concludes the conversation, saying "the die is cast." Consequently, Stahl fired Massar's weapon shortly afterwards, as it destroyed almost every ISA ship in orbit, and had separated Lucas and Echo from each other.
However, Sinclair survived and managed to board Stahl's base, eventually making it to Stahl's Sanctum, killing Stahl and shooting Lucas in the chest, mortally wounding him. After informing the Ground team that he found Massar's weapon, Sinclair looks down on Lucas, disappointed with his betrayal and treachery. He also revealed his intentions to Lucas that he actually intends to restart the war against the Helghast and plans to use Massar's weapon to finally eradicate the Helghast threat. After discussing his plan, Sinclair apologizes to Lucas that he couldn't be the person to protect him before executing him with a shot to the head.
A month later, Sinclair returned to Vekta as a "hero" and began rallying the Vektans in Vekta City in a speech in support for war against the Helghast. However, during in the middle of his speech, Sinclair was assassinated by Echo with her StA-61 Rifle, thereby avenging Lucas' death, and preventing a new war between Vektans and the Helghast from beginning.
Like most Vektans' animosity towards the Helghast, Sinclair regarded all Helghast as animals and views the peace treaty between the Vektans and Helghast as a mistake. Half breeds are not spared from his contempt either. Ruthless and calculating, he is shown to go to any lengths to wipe out the remaining Helghast, even so far as betraying and executing Lucas, who he had raised as his son and considered him as such, in order to restart the war after he went rogue and sided with Echo instead of him.
- "Well looks like you're going to stick with me kid. Come on. We'll be okay once we get to the other side of the wall. Come on!"
- "I never thought it would be you to betray me Lucas, be the one I couldn't trust. "
- "You're too important to this operation. Goddammit you're too important to me."
- "Look buddy, I don't like it any more than you, but until we cross the wall, it's their rules."
- "We think it's Helghast encryption."
- "The die is cast."
- "I thought I knew you, Lucas. After everything these sons of bitches have taken from us in the past I didn't think you'd be the one I lost faith in. Be the one I couldn't trust. Everyday New Helghan continues to exist we are under threat. I've shown them that. And now I'll show them how we can remove that threat. Forever. I've always tried to protect you, son. I'm sorry I couldn't be that person."
- "I remember when the Helghast first came to our world, there was a belief that we could coexist. Through their suffering we thought, we saw our humanity. But this was a mistake. We should've realized then, as we do now, that the Helghast chose to forsake their humanity long ago. They are an aberration. They don't share our values. And they don't deserve our compassion. The belief that we could live beside the Helghast was false. We deceived ourselves."
- He is voiced and modelled after British actor David Harewood.
- He seems to distrust politicians, as shown in the beginning of The Shadow.
- Sinclair's background with Kellan is similar to that of Bradley Vaughton with Jan Templar. As Vaughton took in Templar after the death of his father as well.
- His callsign is Pulsar.
- He is the announcer for the VSA in Warzone, alongside his counterpart, Anton Saric.
- He appears to have been wounded rather severely in the war, taking a glancing shot to the head (if his uneven widow's-peak is any indication) and possibly having a bionic arm, given the harness he appears to be wearing in cutscenes.
- According to the Dossier about Sinclair (a collectible which can be found during the campaign), his first name is Thomas. However, in the last mission, "The Savior," there are two TV screens visible from the uppermost level of the park broadcasting Sinclair's speech which state his name as Elliot Sinclair.
- He is the first main antagonist to have killed the main playable protagonist in the Killzone series.
- He is the second antagonist to be killed by the deuteragonist instead of the protagonist, the first being Scolar Visari by Rico Velasquez in Killzone 2.