Zappa and Beefheart got to know each other in high school in Lancaster California, and performed together from time to time, early in their careers. Like Zappa, Beefheart had a great interest in visual arts as well as music. He started out wanting to be a sculptor and produced many paintings and sculptures throughout his life.
I remember when his first major album, Safe as Milk, came out in 1967, friends were comparing it to Zappa's Freak Out!, which had come out the year before. Safe as Milk never became the major icon that Freak Out! was and is, but Beefheart's next big album, Trout Mask Replica, from 1969, is one of the most influential albums of all time.
Here's the band, playing two songs from the album, live in Belgium in 1969:
Beefheart was influenced soon afterward by the free jazz of Ornette Coleman and Cecil Taylor. Here's his band in Detroit in 1971:
And here's a great video from his last album, Ice Cream for Crow. What a crew:
Captain Beefheart and the Magic Band; directed by Don Van Vliet (with much uncredited assistance from producer Ken Schreiber), cinematography by Daniel Pearl (The Texas Chainsaw Massacre); Don Van Vliet (vocals, harp), Gary Lucas (guitar), Jeff Tepper (guitar), Rick Snyder (bass), Cliff Martinez (drums); filmed on location in the High Mojave Desert near Lancaster, California; clip rejected by MTV USA as "too weird" upon release, now in the Permanent Film and Video Collection of the Museum of Modern Art, NYC: