Although there is nothing physically wrong with him, Surridge theorizes that his mind had been warped by the experimentation. Still, his actions seem to maintain a twisted logic to them. The experiments actually yield some beneficial results: he develops Olympic-level reflexes, increased strength, and incredibly expanded mental capacity (as demonstrated consistently throughout the novel, V is a genius in the fields of explosives, martial arts, philosophy, literature, politics, computer hacking and chemistry).
Over time, the man is allowed to grow roses (violet carsons) and raise crops for camp officials. The man eventually starts taking surplus ammonia-based fertilizer back to his cell, arranges it in bizarre, intricate patterns on the floor. He then takes a large amount of grease solvent from the gardens. In secret, the man uses the fertilizer and solvent to make mustard gas and napalm. On a stormy night (Nov. 5th), he detonates his homemade bomb and escapes his cell. Much of the camp is set ablaze, and many of the guards who rush in to see what happened are killed by the mustard gas. The camp is evacuated and closed down. He adopts the new identity, "V", and dons a Guy Fawkes mask and costume. V then spends the next five years planning his revenge on the Norsefire government, building his secret base, which he calls the "Shadow Gallery". He then kills off most of the over 40 surviving personnel from Larkhill, making each killing look like an accident. However, he saves Prothero, Lilliman and Surridge, (the 3 most responsible for the experiments on him) for last, showing only the remorseful Surridge a bit of mercy by using a painless poison.
He doesn't even consider "V" his "name," saying "I do not have a name. You can call me V." The only explanation given regarding V's past is Surridge's diary, which V leaves out in the open for the "Finger" (Norsefire's secret police) to find after he kills her. Inspector Finch, the head of London's police department and one of Norsefire's most powerful officials, reads through the diary, but points out that V wanted them to read it. V also tore out many pages, which possibly left clues to his true identity before arriving at the camp. Finch further speculates that V fabricated the version of Surridge's diary, which he left with her body, just to confuse the police.
In the comic and graphic novel, Delia Surridge states in the diary that he was ugly and possibly deformed, although she mentions "Physically, there doesn't seem to be anything wrong with him. No cellular anomalies, nothing". His confidante Evey Hammond speculates in the comic that V might be her own father, who was arrested years before as a political prisoner; V denies it, however, and Moore has confirmed that V is not Evey's father. There is also some speculation that V could actually be Valerie, the prisoner in the cell next to his whose autobiographical letter inspires V not to give up (and which he later passes on to Evey). However, Prothero and Surridge both describe V as the "man" from room five (V claims Valerie was the "Woman in room four" and also that he did not write Valerie's letter), which would seem to dispel this theory.
As Finch comments on the pages V tore from Surridge's diary, "What was on the missing pages, eh? His name? His age? Whether he was Jewish, or homosexual, or black or white?" He later describes himself to Finch as "an idea." That Evey genuinely takes over the persona upon the death of her predecessor suggests V is something transcending the individual physically donning the mask, akin to Doctor Mabuse or the Phantom. Late in the story, Evey, having taken over V's mission, also appears to consider herself as anarchy incarnate. In effect, V is an Everyman: potentially, anyone oppressed by their government could become a revolutionary avenger.
V stages an attack on the government's propaganda broadcasting station, strapping himself with explosives and forcing the staff to follow his orders under threat of detonating them. V then broadcasts a message to the people, telling them to take responsibility for themselves and rise up against their government. Finally, V destroys the government's CCTV surveillance buildings, eroding its control over British citizens. However, V is mortally wounded when he is shot by Finch, and he staggers back to the Shadow Gallery, where he dies in Evey's arms. Evey then puts him in state, surrounded by lilies and gelignite, in an Underground train that stops at a blockage along the tracks right under 10 Downing Street, where the explosives-laden cab detonates, giving V a viking funeral, as per his final request of her, in the process. Evey then takes on the mantle of "V."
Near the climax of the film, V admits to having fallen in love with Evey. There are strong elements from the The Count of Monte Cristo and The Phantom of the Opera in this interpretation of V that are not as pronounced in the original story. V's history is also very different from that given in the graphic novel; his powers are no longer the result of a hormonal experiment, but an end result of a series of biological weapons experiments.
Another addition to the character's biography is that, prior to his escape from Larkhill, he claims to have forgotten his past in its entirety, including his name, transforming him totally into the "everyman" persona he adopts in both the original story and in the film. When Finch finds Surridge's journal, no torn pages are seen or described.
Unlike the comic book series, where he kills dozens, if not hundreds of government workers indiscriminately, the V of the film kills only to fulfill his vendetta and those who are an immediate threat to his plans. He only bombs two buildings, the Old Bailey and Houses of Parliament building.
V is revealed to have suffered severe burns, whereas in the novel, he is assumed to have been unscarred by his escape from Larkhill (nonetheless, Dr. Delia Surridge describes him as being physically unattractive). In the doctor's description of him as a patient she mentions that there is something "different" about his eyes.
In the end, Creedy and his men supposedly kill V with automatic weapons fire, instead of Finch from the comic book series. V keeps a steady stance during the rounds. When the soldiers run out of bullets, V attacks them all with knives, killing them all, and executes Peter Creedy. It is revealed afterwards that V was wearing a metal breastplate, but some bullets mortally wounded him.
Mortally wounded, V dies in Evey's arms. She places his body aboard the explosive-laden train, which in the film detonates under the Houses of Parliament rather than Downing Street.
Also, in the film it is not specified whether Evey takes on the role of V. But the final scene in which she is standing on the roof conversing with Finch implies a sense of closure and conclusion, which connotes that it's "all over", so to speak.