I think that Jackie Mason is one of American's greatest comedians. Jackie Mason has a long career and reputation as being an iconic entertainer in the industry. And he has garnered a lot of fans because of it. That is why it is only logical to suggest he is one of the greatest comedians.
Times were very different when Jackie Mason got his start as a comedian. He was considered very "risqué" . People went to see him because he was "naughty" and said things that most people were thinking but would never say out loud. Over the years society changed and some comedians found a need to simply go on a stage and spew profanity. Over the many decades that Jackie Mason has been performing, he has been true to his beginnings and maintained the same level of caustic humor, which makes him absolutely one of the greatest.
The modern comedic enterprise is built on the shoulders of a lot of comics from the 1950's and 1960's, many of them Jewish, who appeared on the variety shows of the time. Jackie Mason was one of these and he began a tradition of self deprecating and very honest humor.
No, Jackie Mason is not the first name that I would suggest for the greatest American comedian, simply because the name is not familiar to me. Without doing an Internet search, I would have no way to determine his impact on American comedy, which indicates to me that he is among the greatest. Instead, I would suggest the comedic couple of Desi Arnez and Lucille Ball.
I do not think that Jackie Mason would be one of the greatest American comedians. I do not even know who they are so it would be hard for me to think of them as a great comedian. I like other comedians a lot too so they would have a lot of competition for the spot.