Breath of Fire.
The Stone Robot originally stands far north of Tantar and Tuntar. After Ryu, Nina and Bo manage to rescue the Chief of Tuntar from the Dark Dragon Fort, their next task is to destroy the rock that the Dark Dragon's have used to block the river. For this, they are advised to use the Stone Robot.
Entering from the left leg, it is fairly simple to walk up to the pelvis, and from there, the torso of the robot. Near the heart, the party are challenged by the Dark Dragons set to guard it, but defeat them easily. Using the key on the heart, they progress to the brain, where Nina is able to command the robot to destroy the rock. For a few seconds, the Robot becomes a playable character on the world map. When the player (as the Stone Robot) reaches the rock, a cut scene wherein Nina orders the Robot use its laser on the rock is initiated. With the river flowing once again, the party exits the craggy automaton.
Later, as Tantar and Tuntar celebrate a marriage between two of their citizens, another General uses the Stone Robot to destroy the (fortunately, abandoned) Tuntar. As he attempts to destroy Tantar, the Robot freezes. Ryu, Nina and Bo take this opportunity to make their way inside the Stone Robot again, challenging the General near the brain.
After the battle, the robot heads towards the volcano south of Tantar and Tuntar. It allows the party to leave before climbing in, effectively destroying itself. This causes the magma to overflow, and it solidifies over the southern river, allowing the party to cross.
Afterwards, Nina says, "There was a quiet voice. It said 'Goodbye...'"
Bo replies "And it asked us not to make the same mistake."
The Stone Robot contains five treasure chests; two in the pelvis (don't think too much about whereabouts in the robot you are at this point) containing a BronzHT and a Herb, and three in the heart chamber. You will need to use the teleporters to reach those.
After using the KngKey on the heart, step on the teleporter to the left of the stairs. Then, ignore the teleporter directly in front of you, and follow the path around to the next one. In this second room, take the far western teleporter to reach the Acorn. Try to teleport back from here, and you will find yourself standing in front of the heart again.
Now, proceed to where you were before, but this time take the eastern teleporter instead. Take the nearest teleporter for two chests, containing a Life2 and a Marbl1. Then use the teleporter to return to the previous room, and this time take the further one. Then you must simply follow the linear path to the brain.
 As a Character
It is unknown who or what created the Stone Robot, or for what purpose. Although he is known as a Stone Robot, when within him, the game identifies him as 'the Giant'. In fact, he is more like a golem than a robot, although he does appear to have a mechanical heart and mind. He shows somewhat of a conscience when he selflessly sacrifices his life for the good of the heroes' journey.