Gene Dynarski, an actor whose roles on episodic TV included the irascible Izzy Mandelbaum Jr. on Seinfeld and the victim of a human bat in a memorable 2000 episode of The X-Files, died Feb. 27 in a Studio City rehabilitation center. He was 86.

Dynarski’s death was announced by friend and playwright Ernest Kearney, who writes on his website that Dynarski had been recuperating from a “mild heart episode” for the last month.

“I had visited Gene only a few days prior,” Kearney writes. “He seemed his old self, ranting on about me finding him a lawyer to sue the rehab-center…I could tell by the glances of the staff passing by his room that Gene had managed to piss them off. Dynarski had a genius for pissing people off. And generally, the very last people whom an actor in Hollywood should piss off.”

In addition to numerous TV credits reaching back to the early 1960s, Dynarski appeared in Steven Spielberg’s Close Encounters of the Third Kind (as the supervisor to Richard Dreyfuss’ UFO-haunted Roy) and Alan J. Pakula’s All The President’s Men (as a court clerk).

But it was in character roles on episodic TV that Dynarski was most prolific, with appearances, as a sampling, in the 1960s (Ben Casey, The Big Valley, The Monkees, Voyage to the Bottom of the Sea, and two episodes of Star Trek), the 1970s (The Doris Day Show, Starsky & Hutch, Kojak) and the 1980s (Hill St. Blues, Star Trek: The Next Generation). He made two appearances in 1997 as Seinfeld‘s overly confident Izzy Mandelbaum Jr. who attempted to hoist a television set only to wind up in a hospital bed next to his dad (played by Lloyd Bridges). Dynarski ended his TV career with 2000’s “Patience” episode of The X-Files.

In 1979, the actor opened The Gene Dynarski Theatre in Los Angeles, a small venue that in its decade and a half existence gave early starts to some future big names, including Ed Harris, Elisabeth Shue and Tom Hanks.

Dynarski is survived by two daughters.