Isaac was one of the antagonists on the show but he wasn’t entirely bad. He’s also dramatically different from his video game incarnation from Castlevania: Curse of Darkness.
But his backstory is very similar to what happened in the Castlevania video games. He worked as a Forge Master, making monsters to serve Dracula. He was definitely the vampire king’s most loyal follower.
And when Alucard, Trevor Belmont, and Sypha Belnades showed up fight Dracula, he creates a magic portal and pushes Isaac through it to save his life.
He spends the last two seasons with the aftermath of his master’s demise. His goal is to get revenge and he builds a very impressive army of monsters to accomplish that.
It was a bit hard to believe that even vampires like Lenore stood absolutely no chance against him. I was going to hold a grudge against him if he actually had killed her.
I thought he was going to kill Hector too but he forgives his friend for betraying Dracula. He manages to kill Carmilla and make himself happy with the outcome.