After a long battle with an unknown illness, Clarence Gilyard Jr. passed away at the age of 66. Best known for his roles in ’80s blockbusters “Top Gun” and “Die Hard,” Gilyard was a veteran scene-stealer.

The UNLV College of Fine Arts confirmed the actor’s death, where he had been working as a film and theater professor.

“It is with profound sadness that I share this news,” Dean Nancy Uscher posted on Instagram. “His students were deeply inspired by him, as were all who knew him. He had many extraordinary talents and was extremely well-known in the university through his dedication to teaching and his professional accomplishments.”

Gilyard reportedly succumbed to a “long illness,” though the details of his death have not yet been disclosed.

Gilyard, born in 1955 in Moses Lake, Washington, made his movie debut as Marcus “Sundown” Williams- an elite fighter pilot- in 1986’s “Top Gun”, starring opposite Tom Cruise.

After playing Theo in Die Hard (1988), the actor would go on to play Hans Gruber’s eccentric computer hacker who commandeers the Nakatomi Plaza’s security codes, opposite Bruce Willis as detective John McClane.

In 2020, Gilyard reprised his role as Theo when he appeared in an Advance Auto Parts ad with Willis. The ad, which hyped the brand’s DieHard car batteries, featured Theo taking McClane on a mission to get a replacement battery for his dead car. The spot was two minutes long and packed with action.

Other than his role in “The Karate Kid Part II” and “Left Behind,” he has also been featured on popular TV shows such as “CHiPS,” “The Facts of Life,” “Diff’rent Strokes,” 227″ and Simon & Simon.

Gilyard had supporting roles in many movies and TV shows, most notably as Conrad McMasters in “Matlock” and as James “Jimmy” Trivette in the Western drama “Walker, Texas Ranger.” In the latter show, he was Chuck Norris’ right-hand man Sergeant Walker.

Gilyard took a position as an associate professor in the theater department at UNLV in 2006.

“I’m wired to teach. And I’m a professional, but the profession has to feed the classroom,” said Gilyard in 2017. “It’s what stimulates my characters, because I’m in touch with people’s lives in the 21st century.”

He continued, “I work best as an artist when I’m in a fertile arena. That means creative and imaginative. Being with all those millennials — I don’t understand what they’re saying, but I’m siphoning off their energy.”

He kept accepting roles even when the challenges seemed insurmountable.

In 2016, Gilyard received recognition for his role as Hoke Colburn in the University of New Mexico’s Neil Simon Festival production of “Driving Miss Daisy.” He starred opposite Sheree J. Wilson, who is also known for her work on “Walker, Texas Ranger.”

In 2018, Gilyard took on the role of high school coach Devin Wade in the “Longshot” section of EA Sports’ football video game Madden NFL.

Decades of professional experience in TV and film didn’t mean as much to him as his work as an educator, according to his peers.

“Some may find it surprising to know that Clarence valued his appointment as a university professor as highly, maybe higher, than his illustrious career as a TV star,” stated fellow UNLV theater professor Nate Bynum. “It was a major goal for him. He loved his UNLV family and, in particular, the students he instructed in his classroom. Gone too soon.”

The loss of the Washingtonian was a blow to his fans and admirers.

“Professor Gilyard was a beacon of light and strength for everyone around him,” UNLV film department chair Heather Addison stated. “Whenever we asked him how he was, he would cheerfully declare that he was ‘Blessed!’ ”

She continued, “But we are truly the ones who were blessed to be his colleagues and students for so many years. We love you and will miss you dearly, Professor G!”

“Clarence Gilyard has passed away,” wrote on Twitter actor Chris Reed. “RIP to a legendary screen presence.”

Christopher Lawrence, a film critic, also gave praise: “This is going to make my annual Christmas viewing of ‘Die Hard’ — which is most definitely a Christmas movie — infinitely more sad.”