Of Muppets and Men: The Making of the Muppet Show, by Christopher Finch (oversized HC with excellent DJ, 1981, $40, which is 1/3 the internet price.)
"When Sesame Street was launched in 1970, Jim Henson's Muppets had been in existence for fifteen years. The Muppets' first successes had come in 1955 when Henson, then still a freshman in college, and his wife-to-be, Jane had devised a show called Sam and Friends which for eight years enjoyed an enthusiastic following in the Washington, D.C., area. Kermit first saw the light of day in 1956 as one of the regulars on that series. From 1957 on, the Muppets made many guest appearances on network shows, and for three years in the sixties one of Jim Henson's puppets, Beowolf the Dog, was the resident comedian on the Jimmy Dean Show. It was because of Sesame Street, however, that Muppet characters like Kermit, Grover, Big Bird, Oscar, Cookie Monster and Bert and Ernie became household names."
Ask to see this book to be found locked in the back room.