Williams, who died Aug. 11 at 63, was celebrated by his widow Susan Schneider Williams and his children Zak, 31, Zelda, 25 and Cody, 22, who shared in the touching tribute with hundreds of family and friends, including his Mork & Mindy costar Pam Dawber, George Lucas, Bette Midler, Jeff Bridges, Ben Stiller, Penny Marshall, Sarah Michelle Gellar and others, including Williams's former wife Marsha Garces.
Close-friend Billy Crystal hosted the ceremony, and Williams pals Whoopi Goldberg, Bobcat Goldthwait and Bonnie Hunt spoke, along with Schneider Williams and his children, as well as his long-time assistant Rebecca Erwin Spencer, a family friend tells PEOPLE.
"The ceremony was such a beautiful tribute and celebration of Robin's life," says the source. "There was so much joy as well as tears. He touched so many, many people's lives and brought so much happiness and light."
Williams's love of life as well as his acting genius, was honored at the event. The program of the tribute included the Ralph Waldo Emerson poem "To Laugh Often and Much."
"One of the most moving parts was when Susan recounted the day they met at the Apple store," the family friend shares. "They smiled at each other from across the room, which turned into a conversation and them becoming best friends from that moment on."
Memories SharedStevie Wonder sang with the GLIDE Ensemble and Change Band while video tributes of Williams – both personal and professional – played on screens around the room. Spencer spoke of her travels with Williams and called him a "beacon of light."
Williams's elder son, Zak, told the audience that even in the darkest times, he would reassure his father, "It's going to be OK," and Williams would respond, "I know," says the family friend.
"There was a lot of laughter but there were tearful moments of sharing those touching memories," says the source. "But they were rounded out with laughter."
Goldberg spoke of her first trip with Williams and Crystal on behalf of Comic Relief to attend a reception with leading policy makers in Washington, D.C. The trio had come up with an inappropriate joke about Senator Ted Kennedy and ended up in a car with him after they had made the joke together – a memory that had the audience laughing. Goldberg also shared how close she felt to her friend.
"Through tears, Whoopi shared what a true friend Robin was and said, 'More than anything, I really liked him,' " the source tells PEOPLE.
Following the 1 p.m. tribute, family and friends gathered at a reception at the Westin St. Francis Hotel Ballroom.
"It was beautiful," says the source. "Everyone there continued sharing their stories of Robin."
The actor took his own life after battling depression and addiction and had recently received a devastating Parkinson's Disease diagnosis.
"Robin's sobriety was intact," Schneider Williams said shortly after her husband's death. "He was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson's disease, which he was not yet ready to share publicly."
After the tribute ended, the family friend says there was a feeling of peace and of "really saying goodbye to Robin."
"He was a genius, beloved by millions," adds the source. "He was also a much loved husband, father and friend. We all miss him so much."