The name Callum is a Scottish Gaelic form of the Latin name Columba, which means "dove." It originated in the early medieval period, likely around the 5th or 6th century AD, when Christianity spread to Scotland. The name was popular among early Scottish saints and monks, many of whom took the name Columba or its variants.

One of the earliest and most famous bearers of the name was Saint Columba, an Irish monk who founded the influential monastery on the island of Iona off the west coast of Scotland in 563 AD. His missionary work played a crucial role in the spread of Christianity throughout Scotland and northern England.

Another notable figure was Calum Cille, a 6th-century Irish abbot and missionary who helped establish monasteries in Scotland and is considered a patron saint of the Scottish Gàidhealtachd (Highlands). His name is an alternative form of Columba, and he is sometimes referred to as Callum or Calum.

In the 9th century, a Scottish king named Calum mac Aillene ruled over the Kingdom of Dalriada, a region spanning parts of modern-day Scotland and Northern Ireland. His name is recorded in various chronicles and annals from that period.

During the Middle Ages, the name continued to be used among Scottish noble families and clans, particularly in the Highlands and Islands. One notable bearer was Calum Mór, a 14th-century chief of the Clan MacGregor, who played a role in the Wars of Scottish Independence against England.

In the 16th century, Calum Cille Mór, a Scottish scholar and poet from the Hebrides, was known for his contributions to Gaelic literature and his translations of religious texts into Scottish Gaelic.

Throughout history, the name has been spelled in various ways, including Calum, Callam, Calym, and the modern Callum, which became more standardized in the 18th and 19th centuries. Despite its Scottish Gaelic origins, the name has also been used in Ireland, particularly in the Gaelic-speaking regions.