George Francis Rayner Ellis, FRS, Hon. FRSSAf, (born 11 August 1939), is the Emeritus Distinguished Professor of Complex Systems in the Department of Mathematics and Applied Mathematics at the University of Cape Town in South Africa. He co-authored The Large Scale Structure of Space-Time with University of Cambridge physicist Stephen Hawking, published in 1973, and is considered one of the world's leading theorists in cosmology. He is an active Quaker and in 2004 he won the Templeton Prize. From 1989 to 1992 he served as President of the International Society on General Relativity and Gravitation. He is a past President of the International Society for Science and Religion. He is an A-rated researcher with the NRF.

Ellis was a vocal opponent of apartheid during the National Party reign in the 1970s and 1980s, and it is during this period that Ellis' research has focused on the more philosophical aspects of cosmology, for which he won the Templeton Prize. He was also awarded the Order of the Star of South Africa by Nelson Mandela, in 1999. On 18 May 2007, he was elected a Fellow of the British Royal Society.