Mariska Hargitay and other Law & Order: Special Victims Unit cast members are mourning one of their own.

Richard Belzer, who played detective John Munch on the NBC series for 15 full seasons after originating the role on Homicide: Life on the Street, died Feb. 19. The actor, who was also a standup comedian and author of conspiracy theory books, was 78.

“Goodbye my dear, dear friend,” Mariska, who plays Olivia Benson on Law & Order: SVU, wrote on her Instagram. “I will miss you, your unique light, and your singular take on this strange world.”

The actress continued, “I feel blessed to have known you and adored you and worked with you, side by side, for so many years. How lucky the angels are to have you. I can hear them laughing already. I love you so very much, now and forever.”

Christopher Meloni, who plays Elliot Stabler on Law & Order: SVU, also paid tribute to Belzer on social media. The actor tweeted a photo of himself kissing his late co-star’s cheek at the comic’s 2001 Friars Club Roast, with Hargitay smiling behind them.