Firmin died at his home in Kent, UK, after a short illness. He is survived by his wife Joan and his six daughters as well as a raft of grandchildren and great grandchildren.
Firmin, who was born in Essex in 1928, was one half of legendary British production company Smallfilms, along with Oliver Postgate. The pair were responsible for creating kids series including Bagpuss, which aired on the BBC, and The Clangers, which also aired on the British public broadcaster as well as Universal Kids in the U.S. He also created Basil Brush with Ivan Owen.
A spokesman said: “During a career spanning over six decades, Peter worked with great skill in a remarkably wide variety of creative disciplines as a fine artist, craftsman and author.
“Of all his work, he will probably be most fondly remembered for the characters he co-created and made. Peter continued to work with great enthusiasm on creative projects right up until the beginning of 2018, most notably on a new series of Clangers, which won a Bafta in 2015.”