Buchanan is a middle-aged man with dark brown hair and blue eyes. He wears a black suit with a red tie.
As Francis Scott Key Fitzgerald once described, Buchanan is the kind who neglects and leaves his comrades in a tight spot by themselves, reflecting how he is willing to pin the blame on his own subordinate to cover up a crime he himself committed. He even buys his way out of being discovered for his crime and bribes Fitzgerald in exchange for his silence.
Despite his pride and befitting the director of a security company, Buchanan is cunning and meticulous with his own safety, having a backdoor code installed in Eyes of God to ensure that he can commit a crime without being found out. Nevertheless, his hubris ultimately led to his downfall, unable to see through Fitzgerald's scheme of exposing him in court.
Some time after T. J. Eckleburg developed the Eyes of God, Buchanan had another engineer install a backdoor code to the identification system without Eckleburg's knowledge, which can automatically cover any face in the surveillance video with another person's appearance. After the engineer completed the programming, Buchanan killed him and overwrote his appearance with Eckleburg's, thereby framing him as the killer.
After T. J. Eckleburg is accused of murdering a co-worker, Buchanan is visited by Fitzgerald and Louisa May Alcott, being offered to clear Eckleburg's crime. Buchanan declines the offer, as he thinks it is pointless in saving a subordinate whose guilt is proven and detected through Eyes of God. The next day, Eckleburg is in court and is immediately labeled guilty.
As the trial holds a recess, Fitzgerald spots Buchanan and accuses him of murdering his worker. He goes on to explain the entire case, noting how Buchanan has a backdoor code installed in Eyes of God that can produce a ghost image of anyone; in his case, Buchanan killed the victim and overwrote his appearance with Eckleburg's, thus making him out as the culprit. Fitzgerald asks to hand over $400,000 and he'll forget everything. Buchanan agrees and writes him a cheque.
Back in court, Fitzgerald bursts in and plays a recorder with Buchanan saying that he'll give him $400,000 if he forgets about the case. After the trial, Buchanan approaches Fitzgerald and goes to punch him, but Fitzgerald uses his ability and blocks his punch. As Buchanan is arrested, Fitzgerald acquires the Eyes of God and Buchanan's company, while Eckleburg now works for him.
- (to Francis Scott Key Fitzgerald) "I knew it… Your eyes… are the eyes of a man who thinks of others' lives as trash."
- He is named after Thomas "Tom" Buchanan, a character in F. Scott Fitzgerald's novel The Great Gatsby. In the novel, he is the wealthy husband of Daisy Buchanan, Jay Gatsby's love interest.