Atisha (AD 982-1054) was a famous Indian Buddhist Teacher, and the author of Lamp for the Path, the first text on Lamrim (the stages of the path to enlightenment).
He was Abbot of the great Buddhist monastery of Vikramashila at a time when Mahayana Buddhism was flourishing in India.
He was later invited to Tibet and his arrival there led to the re-establishment of Buddhism in Tibet.
His tradition later became known as the “Kadampa Tradition”. See the book Joyful Path of Good Fortune for his life story.