The name Killian has its origins in the Celtic and Gaelic languages, derived from the Irish word "cill," meaning church or monastery. It first emerged as a personal name in Ireland during the early medieval period, around the 5th or 6th century AD.

One of the earliest recorded instances of the name Killian can be found in the Annals of Ulster, an ancient chronicle that dates back to the 15th century. The Annals mention a Killian mac Dregain, who was the abbot of the monastery at Iona in the late 7th century.

The name Killian gained wider recognition with the life of Saint Killian, an Irish missionary who lived in the 7th century. He is known for his efforts in spreading Christianity in the Franconian region of modern-day Germany. Saint Killian was martyred around 689 AD and is venerated as the patron saint of the diocese of Würzburg.

Throughout the Middle Ages, the name Killian was popular among Irish and Scottish families, particularly those with connections to monastic communities or religious orders. One notable historical figure with this name was Killian of Leinsker, a 12th-century Irish poet and cleric.

As the name spread across Europe, it evolved into various spellings and forms, such as Kilian, Kilián, and Kiliaan. In the 16th century, the Dutch painter Kiliaan Rombouts (1599-1655) gained recognition for his religious works and portraits.

Another famous bearer of the name was Kilian Ignaz Dientzenhofer (1689-1751), a Bavarian architect who designed numerous churches and palaces in the Baroque style, including the Monastery of Banz and the Benedictine Abbey of Ottobeuren.

In more recent times, the name Killian has been associated with notable figures like Killian Jordan (1904-1989), an Irish politician and member of the Dáil Éireann, and Killian Mullarney (born 1949), an Irish ornithologist and author known for his contributions to bird field guides.

While the name Killian has maintained a presence throughout history, its popularity has waxed and waned in different regions and cultures. Its enduring connection to religious and monastic traditions, however, remains a significant aspect of its rich historical significance.