On which Star Trek series did Stephen Hawking appear playing poker?

Stephen Hawking appeared playing poker on Star Trek: The Next Generation. His cameo appears in “Descent,” the two-part sixth-season finale and seventh-season premiere, first broadcast in 1993.

In the opening holodeck scene, the android Data plays poker with holographic representations of Hawking, Sir Isaac Newton and Albert Einstein. Hawking appears as himself in the simulation, making the scene a playful meeting of three famous scientific minds from different centuries. The poker game is interrupted when the Enterprise crew receives a red alert.

The appearance came about through Leonard Nimoy, who learned that Hawking was a Star Trek fan while connected with a screening of the documentary A Brief History of Time. Hawking visited the set, sat in the captain’s chair and accepted the invitation to appear. A common mix-up is to call him a regular actor or a guest character: he portrayed a holographic version of himself, and the scene belongs specifically to The Next Generation, not Voyager, Enterprise or Deep Space Nine.