Morbius became a particularly sympathetic antagonist in large part thanks to his tragic backstory. He suffers from a very rare blood disorder that is essentially a death sentence, so he tries to apply his considerable knowledge of biochemistry to create a cure for himself and others who might have the same disorder. Instead, that treatment backfires and causes him to develop the powers and limitations of "pseudo-vampirism": he has to consume blood and he's sensitive to light. The transformation also comes with an outwardly obvious cost, as his physical appearance changes to mimic some of the most iconic "vampire" features.
Over the course of his comic book "life," he's gone back and forth from villain to ally a few times. He starts out as an antagonist for Spider-Man and other heroes, but in time, he starts teaming up with them against other threats.
