Thomas Bruce, 1st Baron of Clackmannan
King David II of Scotland, near the end of his life, appears to have regarded Thomas as the next most senior member of the Bruce family, meaning that he was believed to be a male line descendant of Robert de Brus, 1st Lord of Annandale, but his exact relationship to the royal Bruces is unclear. It has been suggested that he was the son of an illegitimate son of Robert the Bruce or Edward Bruce, but there is no clear evidence for this; he may have belonged to a more distant branch of the family.
Thomas was granted land in Clackmannan by King Robert II of Scotland after organising a revolt against the English in 1334. He married Marjorie Charteris of Stenhouse and it is from this line which most Bruces descend, including the current Chief of Clan Bruce, Andrew Bruce, 11th Earl of Elgin. Thomas and Marjorie's children included Robert Bruce, 2nd Baron of Clackmannan.