Sadistic and amoral, Orochimaru wants to learn all the secrets of the world more than anything else. Immortality, of course, is needed for that, and a bit of chaos to keep from getting bored...
Comes in three temporal clusters - young, early, and late. Young Orochimaru still cares for people close to him, but is coming to gradually despise the fragility of human life. Early Orochimaru has stopped caring about others and pursues solely his own advancement. Late-stage Orochimaru has decided that his previous approach was wrong, and looks to improve life for those he's let himself care about as well.