Gary Coleman dealt with a chronic kidney condition for his entire life that required dialysis and multiple transplants, and it's also part of why his growth was stunted, which affected the kinds of roles he could get as an adult. on top of that, he discovered his parents and business manager had mismanaged and spent a huge chunk of the money he earned as a kid, he sued them in 1989 and won a judgment of over a million dollars, but by then a lot of the damage was done. he worked a mix of small acting roles and other jobs later in life, including a widely publicized stint as a security guard, and passed away in 2010 at 42 after a fall caused a brain hemorrhage.
the child star finances getting mismanaged thing happened to so many kids from that era, his case is just one of the more publicized ones
he actually had a pretty good sense of humor about the security guard job in interviews, seemed to have made peace with it more than the tabloids made it seem