Golem is a recurring summon in the Final Fantasy series, originating in Final Fantasy V for the SNES. In this video game, Golem would at first attempt to harm the players, though what you must do here is escape without harming the beast. If you do this, then you'll be able to add it to your list of summons later on in the game where they'll be required to save him from a pack of monsters. In Final Fantasy V Advance, he appears in a random battle along with two other monsters and the player must defeat them without harming him or letting the monsters kill him.
In Final Fantasy VI, also for the SNES, Golem Magicite can be bought at an auction for 20,000 gil. His primary use is to block the attacks of your opponents. After he blocks 5,000 HP worth of attacks, then he'll be dispatched, waiting to be summoned once more.
His appearance varies from game to game, with his most recent one being seen in the image above. In his initial appearance he was just a clump of rocks molded together. To fit the magic meets machine theme of Final Fantasy VI, Golem was a robot of sorts, though featured similarities to his rock counterpart. In Revenant Wings, Golem takes its appearance almost directly from Final Fantasy XII, has an almost tree-like appearance, and walks via his arms.