Langton's ant is a concept found by Chris Langton. The ant starts off in a random direction and steps forward. If the block the ant is on is empty the ant fills the block and turns left. If the block is filled he empties the block and turns left.
Even though the ant starts off randomly. If no previous walls are placed, after 11000 moves the ant reaches a point called the highway. After this point the ant is stuck in a 100 move pattern and never stops. The interesting thing is that the ant reaches the highway no matter how you place the starting walls.