Beloved television actor Ron Glass passed away Saturday, TV Line reports.  Though Glass’ Hollywood career was long and prolific—spanning over three decades—he was perhaps best known for the work he did later in life, particularly in Joss Whedon’s sci-fi show Firefly, and its follow-up film Serenity. 

Although Firefly was short-lived by today’s standards, the Steampunk-influenced space saga gained a cult following thanks to Whedon’s ambitious storytelling, which combined western and science fiction tropes seamlessly. In it, Glass played Shepherd Book, an enlightened preacher who dished out sage advice to the show’s main characters. 

Glass famously hesitated when he was offered the role of Brook, but signed on after falling in love with the material. "The thing that was galvanizing for me was the characters, so the environment was secondary,” he said at the time. "I was happy to see how Book would unfold in that kind of environment and it worked really, really well.”

Many of Glass' Firefly cast mates, along with Whedon himself, took to Twitter to mourn the passing of their former colleague.

The veteran actor began his career in the early '70s, with roles in iconic shows like All in the Family, Hawaii Five-O, and Sanford and Sons. His big break came in 1975, when he landed the role of Sgt. Ron Nathan Harris in the popular sitcom Barney Miller. 

More recently, Glass appeared in several popular series such as Friends, Marvel’s Agents of S.H.I.E.L.D, and CSI. He was 71 years old.