The name Caelan is of Irish origin and is derived from the Gaelic word "caol" meaning "slender" or "thin". It is believed to have originated in the 5th or 6th century AD when Gaelic culture flourished in Ireland.

The earliest recorded example of the name Caelan dates back to the 7th century AD. It was the name of an Irish saint and scholar, Caelan of Inishcaltra, who lived on the island of Inishcaltra in Lough Derg, County Galway. He is said to have established a monastic school on the island and was known for his wisdom and learning.

Another notable figure in history with the name Caelan was Caelan mac Aillila, a 7th-century Irish king of the Uí Cheinnselaig dynasty. He ruled over the territory of South Leinster and is mentioned in the Annals of the Four Masters, a chronicle of medieval Irish history.

In the 9th century, Caelan mac Ailella was an Irish abbot and scribe who lived at the monastery of Iona in Scotland. He is known for his calligraphy and is believed to have transcribed several important manuscripts during his lifetime.

During the Middle Ages, Caelan was the name of a 12th-century Irish bishop and poet. Caelan of Loughcrew served as the Bishop of Ardagh and is remembered for his religious writings and poetry.

In more recent times, Caelan O'Connor was an Irish writer and journalist born in 1920. He authored several books and worked as a newspaper editor, contributing to the literary and cultural life of Ireland in the 20th century.

While the name Caelan has its roots in ancient Irish history and culture, it has also gained popularity in modern times, particularly in Ireland and among Irish communities around the world. However, its usage remains relatively uncommon compared to more widely known Irish names.