‏M.E. Clifton James‏

Served in WWI, and was badly gassed. After the war, took up acting, and was on the London stage in WWII, where he came to the attention of MI5 (British Military Intelligence) by accident. At the end of one nightly performance, he couldn't find the hat that he would normally wear, and so he donned a beret and walked onstage; the audience, thinking that he was _Bernard L. Montgomery_, promptly stood and cheered.