You are probably most likely to have seen Kenneth Williams in the "Carry On" Movies.He usually played one of the lead roles. Small thin man, big nose very nasal voice.
One of his most memorable ones was a Julius Caesar in one with the immortal line, "Infamy, infamy, they've all got it infamy." In the "Carry on doctor / Nurse" type ones he always played the head doctor, (Dr Tinkle) to Hattie Jaques' matron character.
He also did a lot of work on radio, as mentioned before.