John Smothers (April 4, 1930  - April 27, 2019 ) was FZ's bodyguard or 'personal minder' from 1972 to 1984.  Zappa hired him after the 1971 incident in the Rainbow Theatre in London when a deranged man in the audience, Trevor Charles Howell, pushed Zappa from stage, causing him to be hospitalized for several months.
Smothers was an imposing and muscular figure. He appeared as himself in Baby Snakes (1979) and is also interviewed. He said that he used to be a bodyguard for The Rolling Stones, The Beatles, The Beach Boys, Dean Martin, Sister Soul and The Temptations too. 
Smothers passed away in 2019. Arthur Barrow mentioned the following on his Facebook page, regarding his death: "Good bye to bald-headed John. He was great. He referred to the new guys in the band as "Puppies" - a good call, really. When we got to a sound check for a show, he would first make Frank's coffee, then go outside to bust the illegal T-shirt guys, confiscate the shirts and distribute to the band. He had some kind of expandable police baton (sap?) that he would use to scare off anyone that looked threatening near the front of the stage. All he had to do was whip it out with a mean look, and that usually got the message across. I never saw him rough anyone up, but he probably would have if needed. He was basically good natured. I also recall him saying once when we in NY or London, "He's in a bad mood - Gail is coming to town."