Contra is a pretty simple series to wrap your head around. Two buff dudes grab some guns, shoot some aliens, and then probably go home to party with some babes and bros.
However, while the core concept is easy to grasp, Contra is a series that's spanned over 30 years, full of alien butt whooping. Thus, there's more story here than you might have expected, all beginning in the year 2633.
Let's take a look at the Contra timeline:
2633: Contra
In the beginning, there were two burly gentlemen named Bill Rizer and Lance Bean, who totally weren't supposed to be stand-ins for Arnold Schwarzenegger and Sly Stallone. They were soldiers classified as "Contra," a title given to the best of the best by the Earth Federation Government.
A terrorist organization known as Red Falcon attacked, and Bill and Lance were sent in to neutralize them. However, Red Falcon was no mere terrorist group. They were actually an alien terrorist group, which is way worse. After a lot of shooting, our jacked up heroes killed Red Falcon's leader, Emperor Demon Dragon God Java (which is the most stupidly awesome bad guy name ever).
2634: Super C
One year later, the aliens returned and took over a military base. Bill and Lance had nothing better to do, so they were once again dispatched to save the day. They gunned down heaps of alien soldiers, before killing the new leader, Emperor Demon Gava (not to be confused with Emperor Demon Dragon God Java).
They then presumably returned home to drink mimosas and chill with supermodels.
2635: Operation C
The government must have only had enough money in the ammo budget for one soldier, as that's all they sent. It's unclear who actually goes on this mission, but it's either Bill, Lance, or one of two guys named Mad Dog and Scorpion who do all the shooting.
Either way, our lone soldier went up against another terrorist group that possessed an alien cell that needed to be destroyed. This cell was actually an alien calling itself Black Viper, who was also the sister of Emperor Demon Gava, so there was probably some bad blood over murdering her brother. She gets blown away, the day is saved once again, and the Earth Federation Government probably saved some money from only having to send one guy this time.
2636: Contra III: The Alien Wars
Bill and Lance (or Jimbo and Sully in the Western version) were sent in to deal with the returning Red Falcon army, who had launched a full-on assault on planet Earth. They even blew up an entire city Independence Day-style, so this time they were not fooling around.
The two dudebros made it to the alien hive where somehow Emperor Demon Gava was once again alive and in charge. After a long fight consisting of multiple shape-shifting Gava forms, the two defeated the Red Falcon leader, took down the alien hive, and escaped via helicopter.
2636: Contra 4
Taking place six months after Contra III: The Alien Wars, Black Viper had now made her return much like her brother Gava. She had also set up shop on the Galuga archipelago, the original location of the first Contra game.
Bill and Lance, who likely were getting pretty fed up with all this alien business, were pulled away from whatever they were doing to shoot some more bad guys. They were joined by two other Contra soldiers, and the previously mentioned Mad Dog and Scorpion (who were involved with Operation C in some capacity).
The four men slaughtered waves upon waves of alien bad guys before reaching Black Viper at the end of the archipelago. She then transformed into a gigantic monster version of herself, which didn't really mean anything, as she was facing off against four Contra soldiers this time, and got super killed anyway.
2638: Contra: Rogue Corps
This is the new Contra game set to release this year, so we don't know how it ties into the story. We do know, however, that it's set after the Alien Wars, and that pandas were taught how to fire miniguns. So that's canon now.
2641: Contra: Hard Corps
A rogue military group had taken some alien cells from a research base. Thus, a new group of heroes, known as the Contra Hard Corps, were sent after them. The squad consisted of Ray Poward, Sheena Etranzi, Brad Fang, and Browny.
It's important to note that Browny is a diminutive robot that can hover, and Brad Fang is a genetically altered werewolf super soldier with a minigun for an arm (the panda makes a little more sense now, doesn't it?).
The bad guys were led by Colonel Bahamut, a former war hero from decades earlier. He'd since become disenfranchised with the Earth government, and wanted to use the alien cells to build weapons to overthrow the world's leaders. Ray and the gang proceeded to put a stop to his evil plans.
2642-2647: Contra: Shattered Soldier
In the year 2647, a new enemy faction named Blood Falcon had emerged (what is it with these groups and their fascination with falcons?). You'd think that they would just call on Bill and Lance again, however, it's revealed that five years earlier Bill had turned heel, murdered Lance, and then set off a magnetic super-weapon that wiped out 80% of the Earth's population. For his crimes, he was then sent to a cryogenic prison for 10,000 years (seems a bit excessive).
However, Earth was short on badasses, so the government was forced to release him from cryostasis to deal with the problem. He was joined by Lucia, a genetically engineered cyborg super soldier, who was also there to keep an eye on him.
When the two reached Blood Falcon's headquarters, they discovered that the leader was none other than ol' Lance Bean himself. Lance had survived the assassination attempt by implanting himself with an alien embryo, and had sworn revenge on Earth's government. Bill and Lance had their final showdown, and sadly Lance wound up full of holes.
This is where the Contra canon timeline starts to get absolutely bonkers.
You see, with his dying breath, Lance revealed that Bill was actually framed for both Lance's murder and the super-weapon incident by the government itself.
It turned out the reason that aliens were attacking Earth was not because they wanted to conquer it, but because the aliens were actually a defense mechanism left behind by an ancient race known as the Moirai. They had programmed the Red Falcon aliens (including the embryo in Lance) to attack whoever stole their relic, which contained unfathomable power. Also, this relic was stored in a temple on the planet Jupiter, because things weren't insane enough already.
The relic came into the possession of a group known as the Triumvirate, which consisted of three old dudes who controlled the Earth's government. They then fooled everyone into thinking the aliens were just an invading army looking to cause trouble. However, Lance discovered their plot, and they attempted to kill him for finding out the secret. They set off the super-weapon in order to seize control of Earth's government, and made Bill take the fall for everything.
Needless to say, Bill was a little upset about this. He and Lucia reached the Triumvirate, but were too late, as the trio's plan was to use the relic to become gods, which had just come to fruition. Of course, they got a classic bad guy comeuppance, as the relic pretty much just vaporized them instead.
The relic then transformed into a series of monsters for Bill to shoot, and shoot them he did. The relic was destroyed, the aliens were no longer hostile, the Earth was saved, and Bill had several years of tequila shots, and bench presses to catch up on.