"He was one of a kind in the very best sense and a giant in his field," Kenis said.
The hell-raising icon of stage and screen was nominated for eight Oscars before finally being given an honorary award in 2003.
Irish President Michael D Higgins said it was "with great sadness" that he heard of O'Toole's death.
"Ireland, and the world, has lost one of the giants of film and theatre," he said in a statement.
After working briefly as a journalist and a radioman for the Royal Navy he went to study at the prestigious Royal Academy of Dramatic Art, in a class that included future stars Albert Finney, Alan Bates and Richard Harris.
After making a name in theatre, his big break arrived in the form of David Lean's 1962 desert epic "Lawrence of Arabia".