Elizabeth Mainwaring in Dad's Army was, sort of, seen, once. In the episode A soldier's farewell in the fifth series, she is seen as an ominous bulge in the bunk bed in the Mainwaring's air-raid shelter. (She slept in the top bunk.) The conclusion must be that she was a woman of, shall we say, generous proportions.
In the U.S. series Home Improvements Wilson, the next-door neighbour, is never completely seen; his face is always partly or wholly obscured. Normally he had only a few lines in each episode, and all you saw was the top of his head, but in one episode he took a more prominent part; he had been invited to give a speech to the local school, where all sorts of devices (other persons on the platform, the lectern, lights, etc.) were used to prevent a full view of his face.