Sydney Millar CBE (23 May 1934 – 10 December 2023) was a Northern Irish rugby union prop who played for Ballymena RFC and Ulster and international rugby for Ireland and the British Lions. After retiring from playing rugby he became a rugby coach and a rugby administrator. He became chairman of the Irish Rugby Union in 1995 and from 2003 until 2007 was chairman of the International Rugby Board. Former Lions captain Willie John McBride stated that Millar had given "his whole life to the game".

Millar was born in Ballymena in Northern Ireland, the eldest of six children. He spent a period away as a sea cadet.

Millar played at outside-half at school. A highly technical prop, he focused on the set-piece and could play on either side of the scrum at the highest level.

Millar played for his home town club, Ballymena RFC.

Millar first played for Ireland in 1958 and went on to win 37 caps as a prop. This included a four-year gap when he was out of favour. His last international was in 1970.

Millar played 39 games for the British and Irish Lions, including 9 internationals, on 3 tours. Although tighthead was said to be his preference, he packed down at loosehead in both the 1959 and 1962 Lions series. He also played on the 1968 tour.

Millar also appeared 10 times for the Barbarians, including a win over the 1961 South African team.

Millar coached the hugely successful Lions tour to South Africa in 1974. According to Ian McGeechan, Millar was pivotal to the success of the tour.