8. Dr. Julius Hibbert
The Simpsons' good-natured (perhaps a little too good-natured, from the way he guffaws all the time) family physician has been a fixture on the show ever since Bart attempted ride a skateboard across Springfield Gorge in the second season. That makes for a quarter century's worth of Harry Shearer's sometimes chuckling, sometimes earnest Hibbert lines from looking at Bart on a sonogram ("If I didn't know better, I'd swear he was trying to moon us," he said, sounding surprised) to dry one-liners like telling Homer, "You have an absolutely unique genetic condition known as 'Homer Simpson' syndrome." Shearer's Hibbert portrayal was so matter-of-fact and unwavering that he's been one of the show's most reliable characters, even when the scripts got wackier.