Dr. Otto Hasslein is a physicist in the Planet of the Apes movie series, attached to the space flight project that sends astronauts Taylor, Dodge, Landon, Stewart, Brent, and Skipper to the world of the apes. He serves as the main antagonist in the third Apes film Escape from the Planet of the Apes.
He was portrayed by German-American actor Eric Braeden.
Even before appearing onscreen, Hasslein's name is part of the series storyline, as the scientist who proposed the "Hasslein curve" – a form of time dilation possible with the craft used in the movies.
When he does appear in Escape, he explains to a television news presenter his theories of time, and his belief that changing the future may be possible. He analogizes time to be a highway with an infinite number of lanes, all going from the past to the future; by changing lanes, one can change destiny. The theory, known as "many-worlds interpretation", was first advanced in 1957 as "relative state formation" by Hugh Everett, and was popularized in the 1960s and 70s by Bryce Seligman DeWitt who applied its lasting name. Hasslein mentions neither real-life scientist in the film.
Hasslein learns that talking chimpanzees, Doctors Cornelius, Zira and Milo (who was killed by a primitive gorilla shortly after arriving), have actually arrived in the present day (1973 in the movie) from Earth's own future, where mankind has fallen to the level of beasts while apes rose to power and intellect. While the other members of the Presidential Commission appointed to deal with "alien visitors" are initially skeptical of the time-travel story, Hasslein sees confirmation of his theories – and becomes afraid that the pair's presence may somehow set man's downfall in motion. As the American President's science advisor, he expresses his concerns, resulting in Cornelius and Zira first being taken into custody, then interrogated at length.
Provoked by Zira's drugged admissions of her experimentation on humans, and Cornelius giving details of his historical research into man's decline, the Presidential Commission concludes (in a reflection of Taylor's fate before the Ape council in the first movie, with Hasslein in the place of Dr. Zaius) that the couple's unborn fetus should be "prevented" from birth, and that Zira and Cornelius should be "humanely rendered incapable" of conceiving again, with their ultimate fate to be decided later – at Hasslein's determination, though it appears likely they will be handed over either to scientists or the military for study.
When Cornelius and Zira escape military custody (at the beginnings of Zira's labor pains), Hasslein mounts a full-scale hunt, including searches of all local circuses and zoos. Days later, a carpet bag abandoned by Zira turns up, near the derelict shipyard where they have been hiding, and the pair are spotted soon afterward, with Zira carrying a baby chimp, so Hasslein knows she has given birth.
Boarding their ship, Hasslein approaches Zira, pistol in hand, and demands she give him the baby, as the authorities approach. Before they arrive, he shoots Zira, and fires several shots into the swaddling blankets.
Cornelius had earlier asked Dr. Lewis Dixon, who had told the couple about the shipyard as a hiding place, for the means "to kill ourselves" to avoid being captured, and was given a pistol. Heretofore a pacifist, Cornelius now uses the pistol to avenge his wife, shooting at Hasslein from a crow's nest on the ship. As the authorities arrive, Hasslein and Cornelius trade gunfire. Cornelius kills Hasslein, but is himself killed by sharpshooters, falling to the deck.
Despite Hasslein's best intentions, the baby he killed was not the offspring of Zira and Cornelius – and his treatment of their arrival may have just set in motion everything Hasslein hoped to.
- In the novelization of the film, his first name is Victor.
- He is the first main antagonist in the series to be human.