Mel Brooks, who had also written jokes for the Admiral show, was soon added to the YSOS staff. Like the play’s character Ira Stone, he would often arrive late and complain of some ailment. It later transpired, Reiner said, that he was in fact hypoglycemic, which was a source of some of his woes, perhaps including his insomnia.

The play tends to nail each character with a defining characteristic and elaborates on it, sort of like a comedy sketch. But except for a few scenes it doesn’t really deal with the process of writing this show, nor the characteristic contributions of these writers. So the play doesn’t have much to say about Mel Brooks as a writer.

In an archival interview Larry Gelbart described Brooks’ method as creating whole routines, whereas Gelbart was used to throwing in an appropriate line or joke. With Mel, he said, it wouldn’t be “why does the chicken cross the road? To get to the other side.” Instead Mel “would become the chicken, then he’d play both sides of the road, and he’d cross himself, doing 18 choruses of something while he’s crossing it—nobody else does this. He’s the funniest writer—and chicken—in the business.”

One of Brooks’ specialties for Caesar was “the Professor”—an expert on something or other (sleep, archeology, etc.) being interviewed. Carl Reiner was first hired on the show as an actor to be the interviewer. Later the Professor would evolve into the 2000 Year Old Man, which Brooks himself did, with Reiner. It started Brooks’ performing career, which later contributed to the success of his movies.

Carl Reiner became one of the regular sketch actors on YSOS and informally one of the writers, especially for Caesar’s Hour. According to wikipedia, he was the prototype for the Milt Fields character in the play, but I’ve yet to see a reference to Reiner showing up for work in a matador’s cape and a French beret, as Milt does in the play.

As Larry Gelbart explains, comedy writing is based a great deal on improvisation, and Reiner was skilled and imaginative. He was also skilled at “doubletalk--” improvising dialogue in a foreign language with words that don’t necessarily mean anything but sound right, and also funny. Sid Caesar was the acknowledged master, but Reiner held his own in sketches like the satire on the Italian neorealist movie The Bicycle Thief, performed completely in fake Italian.

Reiner with Brooks as 2000 Year Old Man

Reiner was probably with Sid Caesar the longest, and for a long while was identified with him. Though he’s had a career as a performer (most recently in the new Ocean’s Eleven series), he made his enduring mark with the Dick Van Dyke Show. It's remembered for introducing Mary Tyler Moore as Laura Petrie, but Van Dyke as Rob Petrie worked on a comedy show based on the Sid Caesar shows. Rose Marie as Sally Rodgers was again based on Lucille Kallen and Selma Diamond—though this time, more on the harsh voiced, one-of-the-guys Selma.  Reiner also wrote and/or directed several of Steve Martin's early films, from the satiric (and Caesar-like) Dead Men Don't Wear Plaid to the classic romantic comedy All of Me.