Dutugamunu (Sinhala: දුටුගැමුණු Duṭugämuṇu), also known as Dutthagamani duṭṭhagāmaṇī and Gāmaṇī Abhaya ("fearless Gamini"), was a Sinhalese king of Sri Lanka who reigned from 161 BC to 137 BC. He is renowned for defeating and overthrowing Elara, the usurping Tamil prince from the Chola Kingdom, who had invaded the Kingdom of Rajarata in 205 BC. Dutugamunu also expanded and beautified the city of Anuradhapura and projected the power of his native Rajarata region across the island of Sri Lanka.

Due to his significance as one of the most potent symbols of Sinhalese historical power, Dutugemunu's story is swathed in myth and legend. However, many aspects of the accounts of his life have been verified by contemporary inscriptions, and the basic account of his life is generally accepted as accurate.

Dutugemunu's given name was Gamini or Gamani, a traditional Buddhist name still popular in Sri Lanka today. The Mahavamsa describes how as a youth he mocked his father Kavantissa, king of Ruhuna, for refusing to wage war against the powerful invading Elara, the Solee king of Anuradhapura who usurped the throne by killing the native kings. The prince stated that 'If [his] father were a man he would not speak thus' and sent him a piece of women's jewellery. The resulting fury of the king caused many of his friends to flee to Malaya region and the prince himself being dubbed Dutthagamani, meaning "disobedient". After his death, he was referred to as Dharma Gamini ("righteous Gamini"), but it is as Duttha Gamini or Dutugemunu that he is known to posterity.

The Mahavamsa constitutes the major source on Dutugemunu's reign and dedicates some six chapters (out of 35) to his tale. In chapter 22 he is described as being descended from the ancient royal family of Rajarata through Devanampiyatissa's brother Mahanaga. At the time of his birth Dutugemunu's father was Kavantissa, king of Ruhuna, a small kingdom in south-east Sri Lanka outside of the influence of Rajarata in the north; the border between the two polities was the Mahaganga, or 'Great River', possibly the modern Menik Ganga. Kavantissa is portrayed in the Mahamvamsa as 'devoutly believing in the three gems, [and] he provided the brotherhood continually with...needful things'.

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