Answer
The answer is Philip Drummond. Conrad Bain played the role of Philip Drummond on the sitcom "Diff'rent Strokes" from 1978 to 1986, a total of eight seasons. He played the role of Charlie Ross on the sitcom "Maude" from 1972 to 1978, a total of six seasons. Therefore, he portrayed Philip Drummond for two seasons longer than Charlie Ross.