When were the Muppet's first created?

The muppets originated in the early sixties- maybe mid sixties and were a traveling act- not on their own program but a filler act on various TV programs such as Jimmy Dean ( I believe their first venue) Ed SUllivan, etc long before settling down on Sesame Street. as originally configured Kermit was not a true Frog but a ( Frog-Like creature) in ( his) own words- the character was modified to be more froggy over time.