Prince Imperial Sincline is the secondary antagonist of the anime series Beast King GoLion. He is the crown prince of Galra and a half-Altean. He is known as Prince Lotor in the English dub/re edit, Voltron: Defender of the Universe. A dangerous and cunning adversary, his only weakness is the fact that he fell in love with Princess Fala (Allura), who somewhat resembles his mother whom his father, Emperor Daibazaal (Zarkon), killed after begging a favor to pardon the other prisoners but was refused. He plots to overthrow his own father and marry Princess Fala. He is a sly, scheming villain with an unreliable sense of honor, preferring to fight in direct combat over his father's schemes, and is the arch-rival of Akira Kogane (Keith). Like his father, Sincline loses his temper easily and kills his own men with very little provocation. He even killed his own slave woman once when she accidentally spilled some blood wine Sincline was drinking on his leg. When he repeatedly failed to capture Fala, he instead fixated on her identical cousin Princess Amue Of Heracles (Romelle), raping her at least once. After overthrowing his father and aiding his ultimate defeat and death at GoLion's hands, he learns to his shock that Sorceress Honerva (Witch Hagar) was his own grandmother, who despises him for his hybrid heritage and tries to kill him before being killed along with her cat Jaga. In one last confrontation, after killing his own followers for siding with GoLion, he decides to take Ryou (Sven) as a hostage. While attempting to destroy GoLion to avenge himself of his previous defeats and rule the universe, an enraged Ryou stabs him and they both fall to their deaths.
In the english dub, Prince Lotor's motive for marrying Princess Fala (renamed Princess Allura) was originally so he wouldn't have to fight battles to conquer her planet, but becomes obsessed with her. In fact, he has many daydreams about marrying her and making her his queen consort, and most of his plans since meeting her involve capturing her. Voltron eventually saw a third original season of Non-GoLion footage which featured different fates for many characters, one of whom was Lotor who survived till the end. In another original movie, Lotor teamed with the forces of the main Drule Empire to create a Super-Ro-Beast, but again ended up defeated by the combined forces of the Lion and Vehicle Voltrons.
In the Voltron Force 2011 show and related comic books, Lotor has succeeded his father, Emperor Daibazaal (renamed King Zarkon), and become the new king of Galra (renamed Doom).
As of Season 1 of the Netflix-exclusive Voltron : Legendary Defender, no version of Lotor/Sincline has shown up, though in an odd twist Lion Pilot Keith Kogane has been hinted to possibly be of Galra heritage.