He-Man a.k.a. Prince Adam is the most powerful man in the universe in the Masters of the Universe franchise.
According to the 1983 animated series He-Man and the Masters of the Universe, and most other incarnations of the franchise, He-Man is the alter-ego of Prince Adam. The son of King Randor and Queen Marlena, Adam appears to be a lazy and unfocussed young man. This is an act to distract from his secret. Chosen by The Sorceress to wield the power of Castle Grayskull, Prince Adam can transform into He-Man by holding aloft his magic sword and saying, "By the Power of Grayskull, I have the power!" As He-Man, he is capable of feats of super strength, and is sworn to protect the world of Eternia from evil forces, especially the wicked sorcerer Skeletor. The only people who know He-Man's true identity are The Sorceress, the magical protectress of Grayskull; Man-At-Arms , the Eternian Master of Weapons; Orko , a Trollan magician; and Cringer , a cowardly talking green tiger who He-Man can transform into the mighty Battle Cat. Adam is also the twin brother of Princess Adora, who transforms into the most powerful woman in the Universe, She-Ra. The relationship between Adam and Adora is established in the theatrically released animated film He-Man She-Ra The Secret of the Sword.
in the 1987 film Masters of the Universe , He-Man has no alter-ego, and is the leader of the Eternians battling against Skeletor and his evil army. Along with Man-At-Arms and Teela , the daughter of Man-At-Arms, He-Man attempts to retake Castle Grayskull from Skeletor and free the captured Sorceress. Traveling to Earth, He-Man befrends two teenagers and defends them from evil mercenaries. The noble He-Man gives himself up when his friends are surrounded and outnumbered, allowing himself to be captured and tortured by Skeletor in exchange for his friends' freedom. Despite Skeletor obtaining godlike powers, He-Man was powerful enough to defeat Skeletor in a swordfight to dissipate those powers and force the villain into a deep pit with water at the bottom.
In the 1983 series, He-Man and Prince Adam were both voiced by John Erwin. In the 1987 film, He-Man was portrayed by Rocky IV's Dolph Lundgren. There were two other animated series, either adding to or rebooting the version depicted in the 1983 series. In the 1989 series, The New Adventures of He-Man, Prince Adam was voiced by Doug Parker and He-man by Gary Chalk. In the 2002 reboot series both characters were voiced by Cam Clarke.