"According to the Northern Buddhist school, there are both mortal and celestialBodhisattvas. A mortal Bodhisattva is one who has manifested himself on earth in human (manushi) form, in a series of incarnations, until such a time as he has acquired sufficient merit and enlightenment to receive Buddhahood. Like Gautama Buddha in his incarnation of the arhat Sumedha, the Bodhisattva may have been, in a former re-birth, an arhat bent on his own salvation who, becoming inspired with the desire for Bodhi in order to save mankind, renounced his arhant-ship."