The given name Raegan is a variant spelling of the Irish name Riagain, which is derived from the Old Irish word 'ri' meaning king or royal. It has been in use since the medieval period in Ireland and parts of Scotland.

The earliest recorded example of the name Raegan dates back to the 11th century, where it was found in Irish annals and historical records. It was particularly popular among noble families and clans in the regions of Ulster and Connacht.

In the 16th century, Raegan O'Donnell (1575-1641) was a prominent Irish chieftain and leader of the O'Donnell clan, who played a significant role in the Nine Years' War against English rule in Ireland. His name was recorded in various contemporary accounts and chronicles.

Another notable bearer of the name was Raegan O'Hara (1680-1754), an Irish poet and bard from County Sligo, whose works were preserved in manuscripts and oral traditions of the time.

In the 19th century, Raegan MacNeil (1815-1887) was a Scottish historian and writer, known for his works on the history of the Clan MacNeil and the Hebrides Islands.

During the 20th century, Raegan O'Brien (1920-1998) was an American actor and performer, who appeared in several Broadway productions and television shows in the 1950s and 1960s.

While the name Raegan has its roots in Irish and Scottish history, it has gained popularity in recent times as a gender-neutral name in various English-speaking countries.