Saint Cathan, also known as Catan, Cattan, etc., was a 6th-century Irish monk revered as a saint in parts of western Scotland. He appears in the Aberdeen Breviary, Walter Bower's Scotichronicon, and the Acta Sanctorum, and a number of placenames in western Scotland are associated with him. He is said to have been one of the first Irish missionaries to come to the Isle of Bute, then part of the Irish kingdom of Dál Riata. Very little is known of him; he is generally only mentioned in connection with his more famous nephew Saint Blane, who was born on Bute and later proselytized among the Picts. Both saints were strongly associated with Bute and with Kingarth monastery, which became the center of their cults.
A number of churches were dedicated to Cathan across the western islands of Scotland, including the ruined St Cathan's Chapel on Colonsay. Other churches, now mostly lost or in ruins, stood at Luing, Gigha, and Lewis, the latter of which is said to have once housed his relics. His name survives in the various toponyms in the area containing the element Chattan (where the first consonant is lenited), such as Ardchattan ("Cathan's Heights") and the many places called Kilchattan ("Church of Cathan"). Examples include the names of the hill of Suidhe Chattan and of the village of Kilchattan Bay, both on Bute. His name may be further connected to the Chattan Confederation, a coalition of Scottish clans. His feast day is May 17.