Śāntideva was an North Indian Mahāyāna Buddhist monk associate with Nālandā monastery, who flourished somewhere between 685 and 763 CE. His two extant works are widely considered to be classics of explication of the philosophy and practice of the Buddhist "Great Vehicle" path.
Read after you have read Bodhicaryavatara (or don't). Extremely rich and detailed compendium of how to live a good life and prepare oneself for the next one. I read it from the perspective of outside Buddhism, moreso as a manual of power. Give yourself up and you become infinite, whodathunkit?