Because it popped into my head and I had to write it down.
Iron Hoof was the greatest conqueror to ever live. No army could stop him. No kingdom could resist his advance. Until Equestria. Until he found one pony who had prepared his entire life to resist the Iron Hoof.
…though, to be fair, that one pony had been expecting the iron hoof in question to be more metaphorical. However he wouldn’t let it stop him from doing his duty.