The word "tulpa" comes from Tibetan Buddhism, and is a type of Thoughtform which, once created, assumes an existence independent of its creator. Tulpas are generally created by the experience of extreme emotions, and once manifest can be extremely difficult (and sometimes "impossible") to destroy. Those that are created intentionally tend to follow the pattern of fulfilling their duties as expected at first, gradually adopting methods outside their intended parameters, and eventually either fulfilling their goals in ways that are compleatly outside their creators wishes or ignoring them compleatly. Tulpas are not always "bad" but they almost invariably become troublesome.
A tulpa may also double as the magician who created it, employed for protective purposes by appearing instead of its creator. A tulpa should be distinguished from a tulku, which is either the reincarnation of a saintly individual or the incarnation of a non-human entity, such as a god, demon, or fairy.
Encyclopedia of Ancient and Forbidden Secrets
Encyclopedia of Occultism & Parapsychology