Hamill wrote a touching tribute column in the Hollywood Reporter, recalling how they first met and their friendship over the last few decades.
"I was just bowled over," he remembers of their first meeting before filming "Star Wars." "I mean she was just so instantly ingratiating and funny and outspoken. She had a way of just being so brutally candid. I'd just met her but it was like talking to a person you'd known for 10 years."
He recounts anecdotes about discovering they were famous and how she told stories about her celebrity parents, Eddie Fisher and Debbie Reynolds (who died a day after her daughter). And he writes about doing "crazy things" to amuse Fisher.
"Making her laugh was always a badge of honor."
Hamill also feels grateful that they "got to have this second act with the new movies." Both appeared in "Star Wars: The Force Awakens," though Luke only popped up briefly at the end. It seems likely that he and his sister will reunite in "Episode VIII."
"I think it was reassuring to her that I was there, the same person, that she could trust me, as critical as we could sometimes be with each other," he says. "We ran the gamut over the years, where we were in love with each other, where we hated each other's guts. 'I'm not speaking to you, you're such a judgmental, royal brat!' We went through it all. It's like we were a family."
Want more stuff like this? Like us on Facebook.