Moore died Wednesday at the age of 80.
"First time I saw Mary Tyler Moore was when I was auditioning to find a girl to play Laura Petrie," Reiner said. "I already found Dick Van Dyke. Casting Dick Van Dyke to play Robert Petrie was easy--most talented man I ever met. When I had to cast Mary, the part of Laura, I was at my wits-end. I had auditioned literally 23 or 27 girls and I told Sheldon Leonard, our executive producer, 'I don't know what I'm looking for.' I said, 'None of these girls seem to work.'"
"She walked into the room, I looked at those eyes, the smile and those legs and I said, 'I found her,'" Reiner recalled. "I wanted to see if she could talk, so I gave her a script...she read one line, the first line and I heard this intelligent ping...and I said, 'That's it.'"
From 1961 to 1966, Moore portrayed Laura, the stay-at-home mom to Richie and wife to Rob [Van Dyke], who was head writer for a fictional television variety show called "The Alan Brady Show."
"Dick was a little nervous about the fact she was 23 and he was 30-something," Reiner said. "There was a 12-year difference or something and he was very worried about that and I said, 'Nobody's going to notice.' And nobody ever mentioned the fact that they were not a couple. They were a couple from the moment they kissed in the main title."
Although Moore had never done comedy before, Reiner said the young actress held her own--even coining her own catchphrase, "Oh Rob!" on the show.
"That became a thing," Reiner said. "People were saying that, even if their husbands weren't Rob."
"She did come to me with problems and things and I was her father figure," Reiner said. "It meant a lot because I was a father. I had three children who had a great mother figure and so I knew about what people need when they come to you for anything."
With Moore making a name for herself on "The Dick Van Dyke Show," Reiner often worried that Broadway or film directors would "steal her away." On the contrary, Moore ended up with a self-titled gig, "The Mary Tyler Moore Show."
"When I saw that first opening, even her just going through the street, looking like a real person, but a solid, real woman who knew her place in the world, we knew we were home-free," he said. "Saturday night was her night and nobody didn't watch 'The Mary Tyler Moore Show.'"
Reiner said Moore leaves behind a legacy for all women fighting for equal rights. He said, "She was the first single, working woman who set the template for all women to aspire to and a lot of women not only aspired, but accomplished that. So, the tip of the hat to her."
"She was a very beautiful person, inside and outside," Reiner said.