My parents. Asked me to upend my job and life, move halfway across the country to be closer to them as they approached their elder years so I could help them out as their health is slowly declining. They've told me all my life they just don't want to go to a nursing home when they got older.
So yeah, I did it. Me and my parents have issues for sure, but ultimately I love them and they always have done right by me.
I had to adjust a bit, but I work from home and am single with no kids of my own, so it wasn't as difficult as it is for some people I'm sure. But yeah, I have never done as much for any other family member or friend, but if I were given the choice again, I'd do it all again in a heartbeat.