Thanks to his hit sitcom Diff’rent Strokes, Gary Coleman was the biggest child star in the world. Unfortunately, that was a title Coleman held for many more years than he’d intended.

Coleman was 10 when he was cast as Arnold Jackson, one of two orphans taken in by the wealthy Mr. Drummond. Arnold’s older brother Willis, played by Todd Bridges, grew into a young man over the course of the show’s run from 1978 to 1986. But while Willis was dating Janet Jackson, getting into trouble and planning a move out of the Drummonds’ deluxe condo, Arnold seemed perpetually stuck in the fourth grade.

That was largely due to Coleman’s physical appearance. He suffered from a kidney condition and the medication used to treat his ailment stalled his growth, leaving him 4-foot-8 even as he approached 18 years old. He still looked like a cute, chubby-faced kid but he didn’t feel like one.