Q:What is the last name of the person who explains the history of the Sentinels?  Answer the above question based on the context below:  In the year 2023 in a dystopian future, Sentinels have been programmed to identify and hunt down mutants and any humans who dared to help them. A small band of X-Men survivors is attacked, and Kitty Pryde sends Bishop's consciousness back in time a few days before the attack, to warn the others as to ensure their survival. The group later meets Professor Charles Xavier at a remote Chinese temple, where he explains the history of the Sentinels, which were designed by Bolivar Trask, whom Mystique assassinated in 1973. Alarmed by Trask's death, the government forces captured Mystique and experimented on her, using her DNA to advance the Sentinel program, thus allowing them to adapt to nearly every mutant power. Xavier and Magneto plan to use Pryde's ability to prevent Trask's assassination and prevent the apocalyptic future. But since Xavier would not survive going back decades, Wolverine volunteers, since his regenerative powers would allow him to survive the process. After awakening in his younger body in 1973, Wolverine arrives at the X-Mansion, discovering that the school has been shut down for years due to many students and staff being drafted to the Vietnam War, and that Erik Lensherr was arrested for killing John F. Kennedy. A young, broken Xavier turned to alcoholism and has shunned his mutant powers by using a specialized serum that suppresses his telepathic abilities in order to walk. Hoping to reunite with Mystique, Xavier agrees to help Wolverine and breaks Lensherr out of his prison cell under the Pentagon, aided by Hank McCoy and Peter Maximoff.
A:
Xavier