William Dunbar is a member of Team Lyoko and a ninth grader at Kadic Academy. He is mostly known for being Ulrich Stern's primary competitor for Yumi's heart. Presumptuous and snide, William is commonly treated as a minor adversary to the Lyoko Warriors, despite becoming one in the end.
William arrived at Kadic Academy in New Order because he was kicked out of his old school for sending love letters everywhere. He enrolled in the ninth grade, quickly taking a liking to Yumi. However, due to his jerky attitude and need to outdo Ulrich constantly, Yumi liked him less and less, although it is still implied he has a crush on her.
William's personality is self-centered and overconfident, but still caring. It is often indicated most things he does are done to improve his social status. He constantly strives to outdo others in whatever they seem to be doing. Thus, William could be treated as the opposite of Ulrich, whom he doesn't seem to think of as that large of a threat to his fancy and pursuit of Yumi in romantic fashion. William, due to his brash nature, might sometimes harm others without meaning to. For example, in Final Round, he challenged the Scyphozoa to a battle, losing, but only in an attempt to prove himself a good Lyoko Warrior. William might suffer from inner low self-confidence, but if this is so, he constantly wants to regret this and best his schoolmates. However, he does act more mature in certain situations. For example, in Attack of the Zombies, William did all he could to protect the remaining students from being zombified and wouldn't let anyone leave for their own safety, though in doing this he delayed the Team Lyoko group from getting to Lyoko but he meant well. In The Secret, William helps the Lyoko Warriors tremendously in their fight against XANA, doing everything except going to Lyoko himself. After this, Team Lyoko held a vote about whether or not William should be allowed to become a Lyoko Warrior. (In order for him to get in, it had to be a unanimous vote.) However, Yumi voted against him joining because she felt that he could not be trusted, and he supposedly forgot all about it after a Time reversion. However, it seems that he began to dream about the incident afterwards.
Yumi still does not think that he can be trusted in Double Trouble, but she changes her mind by the end of the episode after he helps out once again, and asks him to join their group. He accepts, and, in Final Round, is virtualized onto Lyoko.
On Lyoko, William is dressed in silver-black armor with a red belt. His weapon is a large sword which can fire energy beams that act like razors, although because he first exhibited this ability while possessed by XANA, it might be that this was XANA-induced, and not actually a genuine power. His sword is quite heavy, although it is powerful, and it can cut monsters in half quite easily (or at least, cut Creepers in half easily).
Like Odd, William seems to enjoy fighting monsters on Lyoko more often then not, perhaps a bit too much... On his very first mission to Lyoko in Final Round, his desire to keep fighting monsters led him to pick a fight with the Scyphozoa all by himself, although Jeremie repeatedly told him to run away. This led to William being possessed by XANA, who used him to completely destroy Lyoko. He is still very much under XANA's control, and XANA uses him do to his dirty work.
After being possessed by XANA his costume on Lyoko changes into an all black body suit with red outlines and has a spiked gauntlet on his left arm that is capable of deflecting Odd's laser arrows and guarding against Ulrich's sabers. And unlike other people who are possessed by XANA, William's eye of XANA does not appear in his eyes, it appears on his forehead and on his new outfit, symbolizing a more powerful possession. XANA has made William the general of his army of monsters and has even given new powers. However, when William appears in the real world in XANA possession (not as a spectre, though), he will have the eye of XANA in his eyes.
In the episode The Lake, William faces off against Yumi on Lyoko. He initially gains an advantage, and is about to devirtualize her when she desperately reminds him that he is a Lyoko Warrior. He reacts, having flashbacks to when he was initiated into the group, in the way that Aelita had memories of her past. He seems to momentarily break free of XANA's control, but eventually succumbs to his influence again. This is the first instance of one of XANA's possessed slaves exhibiting free will, if only a bit. It also shows that William is not following XANA willingly.
William is known to be able to move swiftly through Network easily, but XANA made him his own personal Nav Skid, the Rorkal, which does not attach to the Skidbladnir. He needs it in order to attack Team Lyoko while in the Network, because all he can do is just pass through it; he can't affect it like Franz Hopper can.
William is finally set free in Down to Earth thanks to a program Jeremie created. The program required William to be devirtualized so it could activate. Thanks to Odd, that happened. Afterwards he replaced his clone at Kadic and his affection for Yumi resurfaced. In Fight to the Finish he wants to gain the group's trust back. However, all but Aelita was wary of trusting him again. So he remains in the lab with Jeremie. This, however, turned out to be a huge mistake as XANA takes this chance to possess William (again) and fight off Yumi and Ulrich. However, this one was very short as XANA was destroyed, returning William back to his old self.
In the episode Echoes before the gang is about to shut down the supercomputer, William's last appearance was seen talking to Yumi, and they seemed to be on good terms, again.
- ID Card: William's ID card has a black triangle with a line spiraling out toward the middle, like on his sword, before XANA possession. During Season 4, his card has a black Eye of XANA, also like on his sword, but after possession.
- Health: Unknown (more than 100 Lp. A debate has been going on over this, because in the episode, Cold Sweat, Aelita hits him with an Energy Field, and he was not Devirtualized.)
- Zweihander - William's primary weapon, this huge sword can fire blades of energy and devirtualize anyone hit by it instantly.
- Lyoko Powers (While under XANA's control):
- Super Speed
- Super smoke
- Far Sight (Tentative name)
- William's Tower Activation
- Control over Xana's monsters.
- Can summon his sword back to him if they have been separated
- Tarantula Riding
- Vehicle - Black Flying Manta.
XANA also made him a new version of a NavSkid called the Rorkal.
- William is the newest addition to Team Lyoko.
- It is now and forever unknown whether William's costume reverted back to the silver suit or remained black due to his lengthy possession by XANA. Even his Lyoko avatar no longer shows the silver suit he wore previously, which suggests that he may still have the black suit.
- William's Eye of XANA isn't in his eyes like when most other people are possessed; he has it on his forehead, signifying his mostly being under XANA's total control.
- William produces red ripples upon entering a Tower.
- William became the "cool joker" at Kadic after he got suspended from his old school for sending love letters everywhere.
- Even Jim thought he was "cool" and wanted him in charge of the wreck room.
- He's Ulrich's rival, thus, the foil of Sissi.
- He was the only member of Team Lyoko who did not join the others in shutting down the supercomputer.
- He's the only main character (other than X.A.N.A.,) to not have a cutscene.
- His first name comes from Sir William Wallace, and his last name comes from one of his battles: The battle of Dunbar which he was heavily defeated by the english.
- In Final Round, William had the ability of Super Speed. He never possed these ability when he was under X.A.N.A control. It was possible replaced by Super smoke.