American drama critic and author George Jean Nathan (1882-1958) wrote in Encyclopædia of the Theatre (1940):
 
“An actor without a playwright is like a hole without a doughnut.”
 
In other words, an actor is nothing without a playwright providing the lines. Nathan’s saying has been included in many quotations websites.
 
   
Wikipedia: George Jean Nathan
George Jean Nathan (February 14, 1882 – April 8, 1958) was an American drama critic and editor. He worked closely with H.L. Mencken, bringing the literary magazine The Smart Set to prominence as an editor, and co-founding and editing The American Mercury.
 
Google Books
Encyclopædia of the Theatre
By George Jean NATHAN
New York, NY: A.A. Knopf
1940
Pg. 396:
19. An actor without a playwright is like a hole without a doughnut.
 
Google Books
Broadway Babylon:
Glamour, Glitz, and Gossip on the Great White Way
By Boze Hadleigh
New York, NY: Back Stage Books
2007
Pg. 27:
About improvisation he (George Jean Nathan—ed.) felt, “An actor without a playwright is like a hole without a doughnut.”
 
Known to friends as difficult, to others as impossible, Nathan held that “No chronically happy man is a trustworthy critic.”
 
Froogville
MONDAY, JUNE 18, 2007
The Monday bon mot
“An actor without a playwright is like a hole without a doughnut.”
George Jean Nathan (1882-1958)
 
I recently went to see a “play” that had had no discernible writing expended on it; the entire evening was a doughnut-less hole.
   
Google Books
Drop Dead Chocolate:
A Donut Shop Mystery
By Jessica Beck
New York, NY: St. Martin’s Press
2012
Pg. ? (before page 1—ed.):
“An actor without a playwright is like a hole without a doughnut.” —George Jean Nathan