According to the film He-Man She-Ra The Secret of the Sword, Skeletor came to Eternia via a dimensional portal along with his former master Hordak, leader of the Evil Horde. After he was captured in an attempt to kidnap the newly born royal twins from the Palace of Eternia, Skeletor sold out his master, leading Hordak to flee Eternia with only one of the children, Princess Adora. Afterward, Skeletor dedicated himself to raising his own evil army to conquer the universe, and overthrow the Horde.
In He-Man She-Ra A Christmas Special, Skeletor is charged by Horde Prime, the leader of the Evil Horde that was invented when Hordak messed up too often, to capture two Earth children that had been transported to Eternia. Horde Prime beleived that if left unchecked the children would spread Christmas spirit which could threaten the evil plans of the Horde. Skeletor competed directly with Hordak to be the one to bring the children to Horde Prime, but in the end he was overcome by Christmas spirit himself and rescued the children before they could be destroyed. He even saved a robot dog, as if that weren't enough.
Skeletor uses both dark magic and science nearly interchangably in his plans. He is just as likely to blast his enemies with magic bolts from his ram's headed Havoc Staff as he is to impliment a new experimental technology. He is nearly as skilled a swordsman as He-Man, but is primarily a threat to Eternia due to his intelegence, often preferring to send his minions to do the work of a clever scheme. This intelegence is relative, of course, and his plans often are foiled in downright ridiculous and comical ways. He is often seen riding his warrior's mount, a large purple cat named Panthor.In the 1987 film, Masters of the Universe, Skeletor was depicted as a more menacing and less comical figure. Ruling over an army of armored soldiers, he is able to use an invention called The Cosmic Key to invade Castle Grayskull and capture The Sorceress, imprisioning her in a field that drained her magical energy. In the throne room of the castle he waited to open The Eye of Eternia, which could grant him the powers of the universe when Eternia's moon reached its zenith. He successfully defended Grayskull from being reclaimed by He-Man but failed to capture his nemesis. Sending mercenaries after He-Man all the way to Earth, he eventually does capture him and chain him up in the throne room of Grayskull as he gains god-like power. This power fails to thwart He-Man, however, who breaks out of his chains and defeats Skeletor in a swordfight before dumping Skeletor into a deep pit. Skeletor survived the fall, landing in water and vowing to return. With no apparent way to climb, he is presumably still in that pit to this day.
Alan Oppenheimer voiced Skeletor in the original He-Man and the Masters of the Universe series, as well as its direct spin-offs. Academy Award nominated actor and legend of stage Frank Langella portrayed Skeletor in the live action Masters of the Universe film. Later versions of the character were played by Campbell Lane in 1990's The New Adventures of He-Man and Brian Dobson in 2002's rebooted He-Man and the Masters of the Universe.