Mariska Hargitay, like many of her colleagues, wrote that Richard was a dear, dear friend.
"I will miss you, your unique light, and your singular take on this strange world," she shared on Instagram. "I feel blessed to have known you and adored you and worked with you, side by side, for so many years."
RICHARD BELZER, ‘LAW & ORDER’ STAR, DEAD AT 78
Richard Belzer died Sunday at his home in France. (Jemal Countess)
She added. "How lucky the angels are to have you. I can hear them laughing already. I love you so very much, now and forever."
Belzer's cause of death was not immediately known.
"Goodbye mon ami. I love you," Meloni wrote alongside a picture with #TheBelz.
"Richard Belzer was simply hilarious," Billy Crystal wrote. "A genius at handling a crowd. So sad he's passed away."