Walliams, who is best known for his work on the sketch comedy series "Little Britain," co-stars with Michael Gambon in the Pinter play.
Izzard told the British broadcaster's Newsbeat program: "I thought they were very good. I love Michael Gambon and he did great, and I thought David Walliams did great, as well."
"In at the deep end, but he was wonderful. Brilliant on stage, had a wonderful presence and was perfect for the role," Cooper told Newsbeat of Walliams' debut.
Celebrity Families of 2014 [PHOTOS]