"It is said that Golurk were ordered to protect people and Pokémon by the ancient people who made them. It flies across the sky at Mach speeds. Removing the seal on its chest makes its internal energy go out of control."
Golurk first appeared in BW153 when Lexi was in the UnovaVictory Road when it blocked her path. After battling against it, she decided to capture it as a last minute addition to her League team. Golurk was very strong but seemed quite untrained, not really understanding the communication between itself and Lexi.
Despite this, it's appeared briefly since it's initial capture and League Battle, and has been seen to be more well trained and more connected with Lexi.
Golurk is an automaton; meaning it is able to transform into different figurations within itself. It is able to fly at mach speeds by retracting its arms and legs into itself, and is also capable of transforming into a cannon for attacks. If the seal of its chest is removed, it has the capability of turning a city to rubble.