It is only fitting that Revolver Ocelot is the first boss fight in the series. He is the only character to appear in every Metal Gear Solid game, and is perhaps the true icon of the series. This first encounter was dynamic (get it?) and a great way to set off a storyline that wouldn't conclude until Metal Gear Solid 4.
A lot of Metal Gear Solid's most defining boss fights are just two soldiers going at it mano-a-mano. No outside influences, just two people fighting for supremacy. The feud and friendship between Solid Snake and Cyborg Ninja goes back a long time, so it is only fitting that it ends with a fist fight.
This highly dramatic boss fight also introduces Otacon, everyone's favorite otaku.
Not only could Psycho Mantis read your mind (and memory card), players could only defeat him by switching controller ports. Even if you have never played a Metal Gear Solid game, you have heard of this fight and its wacky trick.
The snowfield encounter with Sniper Wolf is an intense affair. This battle is made even greater by the cutscene that follows it, as it is one of the most emotional points of the series.
Vulcan Raven might be the most physically imposing boss in the entire series. Perhaps the only thing bigger than his hulking physique is his M61 Vulcan.
Players fight Vulcan Raven twice – once inside of a tank and later in a freezing warehouse. While both fights are memorable, the final freezing encounter sticks out a bit more.
You get to fight the former President of the United States on top of a collapsing building. Do I really have to say more? This sword fight is the definition of an epic encounter.
The End is arguably the best boss fight in the entire series just because there are so many ways to tackle it. In fact, there are ways to avoid battling the veteran sniper at all! For example, players can save during the fight and return a week later to find The End dead due to old age. This is the kind of insane strategy that only Hideo Kojima could come up with.
Naked Snake's battle with his mentor is the definition of bittersweet. It is a necessary battle to the death, but one that is filled with sadness. The music that plays during this scene helps make it truly iconic.
It was already enough of a trip to see Shadow Moses Island recreated on PlayStation 3, but the boss fight that occurred took it to new levels of fan service. Finally, after battling gigantic weapons of mass destruction during the entire series, Snake finally got to control one for himself. This fight between two Metal Gears plays unlike anything else in the series, and is just an awesome moment.
It is only fitting that Solid Snake's final battle with Liquid Ocelot is a callback to the entire series. From each game's theme song playing to the changing life bars, this battle is an ode to Metal Gear Solid. It would seem a little obnoxious and self-serving in any other series, but instead works perfectly for MGS.