Parākramabāhu I (Pali Mahā Parākaramabāhu 1123–1186) was king of the Kingdom of Polonnaruwa from 1153-86. During his reign from the capital city of Polonnaruwa, he unified the three lesser kingdoms of the island, becoming one of the last monarchs in Sri Lankan history to do so. He oversaw the expansion and beautification of his capital, constructed extensive irrigation systems, reorganized the country's army, reformed Buddhist practices, encouraged the arts and undertook military campaigns in South India and Burma. The adage "not even a little water that comes from the rain must flow into the ocean without being made useful to man" is one of his most famous utterances.

Parākramabāhu spent much of his youth in the courts of his uncles Kitti Sri Megha, Prince of Dakkinadesa, and Sri Vallabha, Prince of Ruhuna respectively, as well as in the court of the King of Rajarata, Gajabahu II. He succeeded his uncle Kitti as king of Dakkhinadesa around 1140 and over the next decade improved both Dakkhinadesa's infrastructure and military. Following a protracted civil war, he secured power over the entire island around 1153 and remained in this position until his death in 1186. During Parākramabāhu's reign, he launched a punitive campaign against the kings of Burma, aided the Pandyan dynasty against the Chola dynasty in southern India and maintained extensive trade relations with China and countries in the Middle East. Within the island, he consecrated religious monuments, built hospitals, social welfare units, canals and large reservoirs, such as the Sea of Parakrama.