Before Soulcalibur, the only thing you could do when you were getting your ass kicked was button-mash, jump up, and back pedal 'til you could back pedal no more. Even if you were playing Virtua Fighter, the first 3-D fighter, you could only move left, right, up or down. Soulcalibur added diagonal movement to the mix, making it much easier to parry attacks and get the jump on your opponent. Also, to accidentally fall out of the ring. Bummer.
Believe it or not, before The Way of the Exploding Fist came out in 1985, you actually had to wear pants if you wanted to play fighting games. But just because you could play in the comfort of your own home didn't mean you could start spending your saved-up quarters on New Coke and Doritos. Exploding Fist was only available on pricey home computer systems like the Commodore 64 and Amstrad CPC. If you think it's tough to afford a system now, just imagine how hard it was back when people thought the words computer and robot were interchangeable. The Way of the Exploding Fist not only inspired designers to create other fighting games for home consoles; it also started a movement for shorter, catchier titles.
It's not the most popular, but Yie Ar Kung-Fu is the Godfather of fighting games. It was the first to introduce characters with different move-sets. Sure, fighting games would have progressed to unique characters eventually, but you've got to give props to the original for setting the pace so early. Can you imagine a world where Sub-Zero had the same attacks as Johnny Cage, Hwoarong was the same as Forest Law, or Ken was just a clone of Ryu?
Forget that last one.