Alistair Dunstin was a redheaded British alchemist who discovered the secret of transmutation, the ability to transform lead into gold.
Indiana Jones and Alistair's twin sister, Alecia, found him in a Fascist encampment in Libya, apparently a prisoner. He faked an escape with Indiana, only to let Leonardo Sarducci - leader of the Fascist quest to find the Stone — apprehend him soon afterwards.
Later, when Indy and his companions managed to escape Sarducci's clutches, Alistair again managed to gain Indy's trust, even getting with him in the subterranean Tomb of Hermes, the fabled resting place of the Philosopher's Stone. However, he betrayed Jones again, letting the fascists know the location of the Tomb.
In the end, miserable with his actions, through the act of Rectification he returned the Philospher's Stone to the Tomb of Hermes, sealing himself inside the crypt after the entrance collapsed.