https://www.cnet.com/news/spider-man-mysterio-heres-how-the-villain-has-evolved-in-the-comics/

Mysterio first appeared in 1964.

Beck tried to frame Spidey for robbing a museum, but ends up foiled and imprisoned for his crimes. He later joined Doctor Octopus, Sandman, Kraven the Hunter, Vulture and Electro in the first incarnation of the Sinister Six, a supervillain group formed to end the wall-crawler (they still failed), in Amazing Spider-Man Annual No. 1 in 1964.