Fred Ziffel is a hobo Barney chases away from loitering on the railroad tracks.
From the same universe, Mr. Drucker is the town drunk in Mt. Pilot, whom Otis befriends when he "runs away". In fact, actor Frank Cady was originally tested for the part of Otis himself, but was determined to not be right for the role.
Griffith is a native Tarheel. Mayberry is a pastiche of Mount Airy, where he grew up. Nearby to Mount Airy is Pilot Mountain, renamed to Mount Pilot for the show.
Being on the show so endeared the state to Frances Bavier that she moved there (specifically to Siler City) later in life.
Howard McNear (Floyd The Barber) had a severe stroke during the run, and upon returning could not walk or stand on his own. He thereafter was always shown sitting or leaning against an object, and would "walk" across the room off camera. When worsening health required him to leave permanently, Floyd retired and the barbershop became Emmett's Fix-It Shop.