The show concerned a mysterious scientist who travelled through time and space inside a TASID, a ship which resembled a pillar box on the outside. (PROSE: No Future) The series had merchandise based on it, (PROSE: Conundrum) and overseas fans in such places as the United States. (PROSE: Return of the Living Dad) One of its most popular stories, produced during the 1960s, was Vault of the Cyborgs. (AUDIO: Klein's Story)
In 1976, the character was being played by Frankie Howerd. During that same year, Bernice Summerfield, apparently unfamiliar with this aspect of 20th century popular culture, encountered the Professor in his own fictional world inside the Mediasphere. Using his TASID, the Professor dropped her off in the real universe. Benny noticed his resemblance to the Doctor and appreciated the character all the more because of it. (PROSE: No Future)
Behind the scenes
It has been suggested that the fictional series was designed as a tribute to the Doctor Who series itself, given the evidence listed above concerning similar running dates, characters and plotlines. It is possible that Professor X would in effect serve to replace Doctor Who in the Doctor Who universe. If that were the case, it's similar to the relationship between Quatermass and Nightshade.