In Rita Gross's Tricycle Retreat, "Buddhist History for Buddhist Practitioners," we have been discussing what aspects of the Buddha's teachings already existed in the time of the Buddha and what aspects were unique ideas of the Buddha. For example, in the teachings of the Upanishads, an important group of texts in Hinduism, it is stated that beneath our superficial self, or ego, that we will find a true self, a soul. In the Upanishads this true self is called Atman. This notion of a permanent soul, which was quite popular in the time of the Buddha, was addressed in the Buddha's teachings on The Three Universal Characteristics of Existence and marks a very important divergence of Buddhism from Hinduism.
From Week 3 of Rita's Tricycle Retreat,