Ciprian Ilie Foiaș (20 July 1933 – 22 March 2020) was a Romanian mathematician. He was awarded the Norbert Wiener Prize in Applied Mathematics in 1995. He was known for his works in operator theory. Foias was born in Reșița, Caraș County, Kingdom of Romania. The Foias constant is named after him. Foias is listed as an ISI highly cited researcher.