This information is courtesy of David Mark Din.
You can also see the annotated Demise of Sincline (see below if you want to know about this....warning, it contains spoilers! It IS a spoiler!) It contains thumbnails and a brief summary of some of the scenes leading to, and including, his "demise."
In the Golion series, Lotor is called Prince Sincline. Apparently, though his father was Zarkon (his species was never named), Lotor's mother was a human. Yes, a human. Apparently Lotor dreamed of her in one episode, though I've never seen it. She also apparently resembled Princess Allura quite a bit....(hmm...you psychology majors out there should go ahead and pick through that).
In Golion, Sincline's first appearance was in episode 14- "The Crown Prince of Hell" ('Yurak Gets His Pink Slip' is the episode name in Voltron). In Golion, he is more far more ruthless than what we see in Voltron. What they didn't show in Voltron was Prince Sincline's ship firing at the people of Arus (killing one woman - no blood and guts in this scene but they cut this out regardless) and then destroying some buildings. We also don't see a scene in which a clumsy slave girl spills the liquid she was pouring for Sincline and the Prince then kills her.
In an episode of Voltron, Lotor is blinded by little missles from the Space Mice's plane. Both Lotor and the not-so-dead Sven fall off a ledge and into the water below...of course, this means that they live to carry on with other episodes. However, in the Golion version, the Sven that falls over the ledge was actually the real Sven's brother, since the real Sven died in the first series when the robeast struck him. Lotor and Sven's brother meet their dooms at the bottom of the cliff (which, consequently, contained NO water at the end).