William Alexander Millar (6 November 1883 – 3 March 1949) was a South African Rugby union player.
Millar was 5 feet 10 inches in height, and weighed 13 stone 2 pounds.
He was badly wounded during the Boer war, and, on returning to Cape Town to convalesce, his recreations were walking, mountain climbing and shooting.
In 1904-6 he steadily improved, till in the last season he was recognised as one of the best forwards in the Western Province.
His omission from the original list of those selected caused some surprise, but Bertie Mosenthal's inability to make the trip gave him a place as first reserve.