Concept:
In Buddhist cosmology and hagiography, the journey to Buddhahood spans countless lifetimes. A "Bodhisattva" is a being who has made a vow to achieve enlightenment for the benefit of all sentient beings. The historical Buddha, Siddhārtha Gautama, is believed to have begun this specific journey many eons ago. The identity of the Bodhisattva who eventually took birth as Siddhārtha is rooted in the "Jataka" stories and the "Buddhavamsa," which detail the previous lives and the initial vow (Pranidhana) made before a preceding Buddha.
Step 1: Understanding the vow of Sumedha.
The story begins many kalpas (aeons) ago during the time of the Buddha Dipankara. A young Brahmin ascetic named Sumedha encountered Buddha Dipankara and was so moved by his presence that he laid his body down over a muddy puddle so the Buddha could walk across without dirtying his feet. At that moment, Sumedha made the firm resolve to become a Buddha himself in the future. Dipankara Buddha then prophesied that after many lifetimes, Sumedha would indeed become the Buddha known as Gautama. Thus, Sumedha is recognized as the "original" form of the Bodhisattva who, after completing the perfections (Paramitas), was finally reborn as Prince Siddhārtha in his last earthly life.
Step 2: Evaluating other celestial and future Buddhas.
• Vairocana: In Mahayana Buddhism, Vairocana is a "Dhyani Buddha" or Celestial Buddha, often representing the "Dharmakaya" (truth body) and the central figure of the Five Wisdom Buddhas. He is not a previous human form of Siddhārtha.
• Maitreya: Maitreya is the future Buddha. He currently resides in the Tushita Heaven and is expected to be the next Buddha to appear on Earth when the teachings of Gautama Buddha have been forgotten.
• Avalokiteśvara: This is the Bodhisattva of Compassion. While a major figure in Mahayana tradition, Avalokiteśvara is a distinct celestial being and not the specific historical predecessor who became Siddhārtha Gautama.