Boudica is a leader of the barbarians that invade Rome. Marius encounters and defeats Boudica, resulting in her retreating. Once Marius and his cohort storm the barbarian hideout, Boudica and her father are taken prisoner. Once meeting with Commodus her father is stabbed to death, resulting with the barbarians killing everyone and Boudica escapes. Boudica then rallies an army composed of hundreds of fellow barbarian tribes in order to exact her vengeance on Rome and Emperor Nero. She and her army then storm the city aided by 'Beasts of war'. During the invasion, Boudica arrives mounted upon an war elephant, however Vittalion manages to kill the elephant using a pilum which results in Boudica falling to the ground. Vittalion and Boudica then engage in a duel whilst Marius reinforces the Roman barricade. Boudica succeeds in killing Vittalion by stabbing him once in the abdomen and again in the back of the chest. Boudica advances further into the city after Marius is rendered unconscious by a barbarian mortar. She is seen once again riding a war elephant whilst attempting to breach Nero's palace but is stopped when Marius kills her mount using a scorpio. The two then fight with Marius eventually overpowering Boudica, forcing her to yield. However Marius hesitates to deliver the killing blow but is spurred on when Boudica tells him "Do it Roman.". Marius then decapitates Boudica and claims her severed head in victory. Marius then gives Boudica's head to Centurion Severus and tells him to "Display this from the highest place you can find. When the barbarians see it, they'll run."
In reality, Boudica was not killed by someone, but commited suicide after a defeat.
The real life Boudica was very unlike the one portrayed in the game. She did lead a rebellion after her daughters were raped and murdered by Roman soldiers before her eyes, but it never left Britain and her entire army was destroyed at the Battle of Watling street. There are different accounts of how she died, including suicide.