Spacewar! was conceived in 1961 by Martin Graetz, Stephen Russell, and Wayne Wiitanen. It was first realized on the PDP-1 in 1962 by Stephen Russell, Peter Samson, Dan Edwards, and Martin Graetz, together with Alan Kotok, Steve Piner, and Robert A Saunders.

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The “a”, “s”, “d”, “f” keys control one of the spaceships. The “k”, “l”, “;”, “‘” keys control the other. The controls are spin one way, spin the other, thrust, and fire. —Spacewar (on PDP-1 emulator) (MIT)

Spacewar was created in 1961. The link goes to a Java applet that’s a fairly faithful recreation of the original: “1)The spaceships have been made bigger and 2) The overall timing has been special cased to deal with varying machine speeds.”