Alexander Forbes Irvine Forbes (April 13, 1871 – May 15, 1959) was a South African astronomer.
He was born in Scotland in Kinellar, Aberdeenshire and came to South Africa in 1896. He returned to Scotland to study but emigrated permanently to South Africa in 1909. He worked as an architect until 1932.
He was president of the Astronomical Society of South Africa from 1942 to 1943.
He discovered the periodic comet 37P/Forbes. He was also one of several co-discoverers of "Comet Pons-Coggia-Winnecke-Forbes", which is today known as 27P/Crommelin in honor of the astronomer who computed its orbit.