An obsession is another trait that can make a character more interesting. It can be just about anything, as long as s/he cares about it a lot. It can be a hobby, a career goal, another person, revenge, or just about anything, provided it’s a driving force.
Obsession and passion go hand in hand. If you want your character to move mountains, there needs to be a strong and very personal reason to do so. You will need to establish what the rationale is behind it for it to be credible. That is what will pull in the reader’s interest and empathy to either root for or against what the character wants. Needless to say, this works for both heroes and villains. The latter need motivation, too, the stronger the better. Note I said rationale not rational. It doesn’t need to make sense, only be enough to push the character and plot forward.