The name Keegan is of Irish origin and is believed to have derived from the Gaelic name Cian, which means "ancient" or "enduring". The earliest recorded use of the name dates back to the 7th century in Ireland, where it was commonly used as a surname.

In ancient Irish mythology, Cian was the name of a legendary warrior and father of the legendary Irish hero Lugh. The name appears in several ancient Irish texts, including the Lebor Gabála Érenn (The Book of the Taking of Ireland), which dates back to the 11th century.

The variant spelling Keegan emerged in the 17th century as an anglicized version of the Irish surname Ó Ciaráin, which means "descendant of Ciarán". Ciarán was an Irish saint who lived in the 6th century and founded several monasteries in Ireland.

One of the earliest recorded individuals with the first name Keegan was Keegan O'Rourke, an Irish soldier who fought in the Battle of the Boyne in 1690 during the Williamite War in Ireland.

Other notable individuals named Keegan throughout history include:

1. Keegan Deane (1623-1691), an Irish Catholic priest and historian.
2. Keegan Barry (1809-1874), an Irish-born American politician who served as a member of the United States House of Representatives from Mississippi.
3. Keegan de Lancie (1828-1900), a French-American stage actor and director.
4. Keegan Michael Key (born 1971), an American actor, comedian, writer, and producer, best known for his work on the sketch comedy series Key & Peele.
5. Keegan Bradley (born 1986), an American professional golfer who has won four PGA Tour events, including the 2011 PGA Championship.

While the name Keegan has Irish roots, it has gained popularity in various parts of the world, particularly in English-speaking countries, and is now used as a given name for both boys and girls.