He was Oscar, the messy member of the Odd Couple, and he was Quincy, the activist coroner.

The article sums up his appeal very well:

"Never anyone's idea of a matinee idol, Klugman remained a popular star for decades simply by playing the type of man you could imagine running into at a bar or riding on a subway with -- gruff, down to earth, his tie stained and a little loose, a racing form under his arm, a cigar in hand."