Ewing is best remembered for his characterization of part-time deputy marshal Clayton Thaddeus "Thad" Greenwood in thirty-six episodes (October 2, 1965 - September 25, 1967) of the long-running CBS western television series Gunsmoke with James Arness.
In his first episode "Clayton Thaddeus Greenwood", Ewing's character arrives in Dodge City, Kansas, the location of the series, from Oklahoma with a warrant he is unable to execute.