Cheka is included in the list of names on the cover of Freak Out!, under the heading: "These People Have Contributed Materially In Many Ways To Make Our Music What It Is. Please Do Not Hold It Against Them". He is also mentioned in the "biographical trivia" section -
OWE OUR EXISTENCE to Mark Cheka for his initial encouragement and sterling example.
Zappa about Cheka
"Don introduced me to a friend of his named Mark Cheka, a 'pop artist' from New York's East Village. Mark was about fifty and wore a beret. He was living in West Hollywood with a waitress from the Ash Grove named Stephanie, who was also sort of beatnik-looking.
The main focus of his work was a group of large paintings that looked like police department pistol targets, designed to be viewed under flashing lights, which gave the illusion that the silhouettes were jumping around. I found this a little baffling -- but what the fuck do I know from art? We hung out and had some laughs, in spite of the targets.
I had come to the conclusion that the band needed a manager, and had thought (Ow! Was I going to regret this one!) that the person required for this important position needed to be someone with an 'artistic background.' Only then, I reasoned, would our aesthetic be properly understood, and, once we had acquired a manager of such sensitivity, our future success in show business would be assured.
So, I convinced Mark to take the mysterious voyage out to Pomona (fifty miles east), where he might listen to the Mothers, live, at the Broadside. What did I know from managing? I told him that if he wanted to manage the group and could get us some gigs to go ahead.
He didn't really know how to do that. What did he know from managing? He brought in a guy named Herb Cohen, who was managing some folk and folk-rock groups and was looking for another act to pick up. Eventually they became joint managers of our band, with a contract negotiated 'on behalf of the group' by Herb's brother, an attorney named Martin (Mutt) Cohen."