Which historical prince became the Buddha and founded Buddhism?

Siddhartha Gautama was the historical prince who became the Buddha and founded Buddhism.

Known after his awakening as Gautama Buddha or Shakyamuni, Siddhartha Gautama lived in the eastern Indo-Gangetic plain, probably during the fifth century BCE, though traditional dates vary. Buddhist tradition places his birth at Lumbini, in present-day Nepal, among the Shakya clan. His father, Shuddhodana, was the clan’s elected leader or ruler, which explains the traditional description of Siddhartha as a prince.

According to later biographies, Siddhartha was raised amid luxury, married Yashodhara, and had a son named Rahula. He eventually renounced palace life after confronting sickness, old age, death, and religious renunciation. After years of ascetic practice, he attained awakening at Bodh Gaya and spent the rest of his life teaching the Dharma across the Ganges region.

Mahavira was the principal historical teacher of Jainism, while Maitreya is a future Buddha and Amitabha is a celestial Buddha in Mahayana traditions. None is the founder of Buddhism in the historical sense.