Who leads a cult?
Undoubtedly there are as many profiles for cult leaders as there are diagnoses in the psychologist's DSM-IV. But a large number appear to be sociopathic (with narcissistic and paranoid elements).
In plain English look for:
profound lack of empathy for others;
a disrespect for social norms and accepted rules of behavior;
a tendency to project one's own faults on other people;
a lack of interest in anyone else's feelings or beliefs;
a high degree of dishonesty and manipulation in interpersonal dealings;
a tendency to see others strictly in terms of one's own needs.
Tobias and Lalich add some further details to the picture:
the tendency to hierarchy;
the drive for power and wealth;
hostility, hatred, prejudice;
superficial judgments of people and events;
a one-sided scale of values favoring the one in power;
interpreting kindness as weakness;
the tendency to use people and see others as inferior;
Bear in mind that frequently the group leader appears to be preaching the exact opposite values. For instance, Do/Applewhite preached love and peace -- yet dismissed nonmembers as "people who sat in front of TVs and scrambled eggs." He enforced the ultimate disfigurement on his male followers, castration. And, of course, his final message was one of the total destruction of the human race and the planet Earth.
It's not unusual for the leader's organization and long-term followers to mirror his sociopathic, narcissistic, and paranoid traits to some extent. Whether such people are attracted to these leaders or the internal pressures of a sociopathic organizations tend to create such tendencies isn't clear.
Are cult leaders insane?
Probably not legally, no.
Think of Charlie Manson: cunning, charismatic, articulate, in total control. Whatever his mental disease, the courts found him guilty in the Tate-LaBianca murders.
After all, it's almost the definition of legal insanity that one's thinking is too distorted to organize one's own schedule, much less a large group of people.
What motivates a cult leader?
Power, money, sex, and approval or other emotional needs are the big four.
Generally because he or she is about to lose power over the group.
Outside interference may threaten the leader, as it did Jim Jones. A number of cults have closed up shop because of massive defections. The leader's impending personal death, real or imagined, may trigger the suicides as appears likely in Heaven's Gate and Waco.
The leaders are so self-absorbed that they cannot conceive of the group continuing on without them.
Sometimes, they are also quite concerned about their place in history -- trying to extend their power beyond death, as did David Koresh with his final apocalyptic writings.