Alexander Roulston Foster (22 June 1890 – 24 August 1972) was an Irish rugby union international who was part of the first official British Isles team that toured South Africa in 1910.

His father was a Relieving Officer originally from County Donegal from whence his mother also hailed.

He went on to play against both Scotland and France in that first ever Five Nations championship and was later selected for the first official British Isles team that toured South Africa in 1910.

On his return to Five Nations rugby he played in every match of the 1911 and 1912 seasons but was absent for the 1913 championship.

In 1914 he returned to play in three of the four matches for Ireland in the final championship before the First World War and was selected in the first championship after the war in 1921, playing his last match for Ireland on 12 March 1921 against Wales.