"The Changeling" is a season two episode of the original science fiction television series, Star Trek, first broadcast on September 29, 1967, and repeated May 17, 1968. It is episode #32, production #37 and was written by John Meredyth Lucas, and directed by Marc Daniels (who was pictured on-screen as "Dr. Jackson Roykirk").

The crew of the USS Enterprise deals with an indestructible planet-destroying space probe. The plot contains similarities to the later 1979 Star Trek film. This episode is one of only a handful in the original series that take place entirely aboard the Enterprise. The others include "Charlie X", "Journey to Babel", "Elaan of Troyius", and "Is There in Truth No Beauty?".

Around stardate 3541.9, the Federation starship USS Enterprise, under the command of Captain James T. Kirk, investigates a distress call from the Malurian star system. Upon arrival, Science Officer Spock reports that all life in the system has been destroyed and Malur, a world with a recorded population of 4 billion, is now devoid of life, including the Federation science team that was on the planet.

Suddenly, the Enterprise's shields activate when a meter-long cylindrical object attacks the ship with an energy bolt equivalent to 90 photon torpedoes. Kirk orders return fire, but the ship's weapon energy is simply absorbed by the object. Kirk then transmits a hail and the object stops firing. Curiously, the object responds and requests in-person communication with the Captain, allowing itself to be beamed aboard the ship.

...
Wikipedia