Backstage at the Kings Theater in Brooklyn one recent Friday night, Nick Kroll and John Mulaney had finished putting on their silver-haired wigs, wrinkle makeup and billowy, threadbare bohemian clothing. These comedians had a few minutes before showtime, and as they relaxed, a familiar aroma began to fill the air: the scent of tuna fish, coming from a large plastic container that Mr. Kroll was emptying onto a slice of bread.

Though pungent, the tuna (and the absurdly large sandwich they would later bestow on an unsuspecting audience member) was crucial, they said, to the roles they were about to play at this Comedy Central showcase.

It has helped take their kvetching, quarrelsome characters Gil Faizon and George St. Geegland, whom they portray in a recurring bit called “Oh, Hello,” from local comedy clubs to cable television and now to an Off Broadway show starting Tuesday at the Cherry Lane Theater in Manhattan.

“Tuna is a vessel,” Mr. Mulaney said. “Tuna is a universal.”

If you appreciate tuna, Mr. Kroll added, then on some level you already understand what’s funny about “Oh, Hello.”