The first two Castlevania games starred Simon Belmont. By the time the third official game in the series came out, Simon had featured in two main games, a proto-Metroidvania remake, and possible an arcade title (depending on who the official hero of Haunted Castle was intended to be). It's no wonder, then, that what the first Game Boy game for the series came out, people assumed it was Simon again. Why wouldn't they? The series had two things consistently in it: Simon and Dracula, and if Dracula came back, presumably Simon had as well.
And yet, the third official adventure in the series, The Castlevania Adventure, starred not Simon Belmont but his ancestor, Christopher Belmont. Set 100 years before the time of Simon, Adventure helped to flesh out lore of the series by showing the Belmonts as a clan of vampire hunters devoted to protecting the lands from evil (read: Dracula).
While Simon and Trevor have both shown up in further games in the series, both sequels to their games as well as the series-spanning Castlevania: Judgment, Christopher did not get the same treatment, only showing up in one further adventure, a WiiWare remake of his first adventure, Castlevania: The Adventure ReBirth.
The Castevania Adventure
When The Castlevania Adventure came out, Dracula's Curse was still a year off from release. As such, the rule that Dracula came back every 100 years had been put into effect. However, since we now view the series from the perspective of all the games released (with strong recommendation from the official Castlevania timeline from Konami, we know that Christopher took up the whip that had been wielded by his ancestor, Trevor Belmont, 100 years before.
When Castle Dracula appeared on its customary place among the mountains of the Borgo Pass, Christopher realized that the evil vampire Dracula -- the one that had been mentioned in the stories of his ancestor, Trevor Belmont -- had returned. It was up to Christopher, then, to take up the whip and go to Dracula's castle, the fight his way through the evils that lay there in the fortress, and take out the demon king.
In the end, Christopher was able to defeat the vampire. And yet, Christopher's adventure had only reached the end of its first chapter. A greater danger awaiting him...
The Castlevania Adventure had one remake, created as a download-only title for Nintendo's WiiWare e-Shop. A remixed, re-imagined game, Castlevania: The Adventure ReBirth featured drastically different music, levels, and gameplay from the original, giving fans of the series a new adventure starring one of the more ignored heroes of the series.
- Castlevania: The Adventure ReBirth (2009, Nintendo Wii)
Castlevania II: Belmont's Revenge
For Christopher, thoughts of Dracula did not return until fifteen years after his first adventure. One day (some might call it fateful if they were writing bad fanfiction), Christopher's son, Soleiyu, went missing. That same day, four mysterious castles appeared around the Romanian countryside. Sensing the two events might have been linked (because, duh), Christopher took up his family's whip a second time.
Venturing to the castles, Christopher found four despicable bosses. Defeating each of these guardians destroyed their elemental castle, and once all four had been destroyed, a hidden fifth castle was revealed -- Dracula's Castle, once again whole.
Exploring this final lair, Christoper found not Dracula, but his lost son, Soleiyu. The younger Belmont had become possessed by Dracula's foul magic, serving as a vessel for Dracula's power. Only by besting his son in battle was Christopher able to rid the boy of the magic, revealing Dracula's shadowy soul. Chasing the soul to the final throne room, Christopher battled Dracula one more. The vampire was defeated, and Christopher was safe in the knowledge that this time his homelands were safe from the vampire's evil.
Castlevania: The Belmont Legacy
In the comic Castlevania: The Belmont Legacy, Christopher is the decendant of the Belmont line, a family in charge of their ancestral lands and the village that's cropped up within. It's been 100 years since Dracula was last seen and most of the populace, Christopher included, doubted that the evil vampire was anything more than a myth to scare children.
Instead of worrying about Dracula, Christopher had more important things on his mind: his impending nuptuals to the lovely Illyana Riktor. A strong woman in her own right, the pairing of Belmont and Riktor made for a match made in Heaven. Although some in the village had wanted either the lord Belmont of the sweet lady for themselves, these two nobels quickly married, ith much celebration among all that lived in the village.
That changed quickly, though, when Dracula did, in fact, rise once more from the grave. Aided by his human servants, Ivan Bartley and neice Sona, the Dark Prince immediately set about evening the score with his enemies, the Belmont family. He attacked the Belmont family crypt, destroying and desecrating the tombs there in an effort to draw out Christopher and get him to do something foolish. When news of this heinous act reached the newlyweds, Chrishopher immediately began gathering a posse together to head out to the ruins of Castle Dracula.
Initially Illyana sought to go with her husband on th adventure, saying that she was just as strong a fighter and wanted to be at his side rather than at home, worried. Christopher forbade it though, fearing the distraction of keeping her safe (despite her being an accomplished warrior) when the fight with Dracula began. Instead he took other aides: butler Deimos along with the Romani warriors Gaspar Totoyan and his granddaughter Pascha. Illyana was ostensibly sent back home to kep watch over the youngest Totoyan, Viktor. Despite Christopher's warnings, though, Illyana did not stay at home, venturing off with Viktor, instead, to prove her worth.
When Christopher and his lot ventured into Dracula's lands they were met by all manner of undead, waves of them that attacked and mericlessly fought at the heroes. Theese were no match for the band fo warriors, led by Christopher wit his family whip, the Vampire Killer. But dring this encounter, Christopher learned a horrible fact: while they battled these undead, IIllyana had fallen into trouble. Dracula had found her and Viktor, attacking the poor boy, ripping open his throat, while stealing Illyana away. Christopher and his men regruped back at the Belmont estate to figure out their next move.
At the home the vampires came for them again, with young Viktor, now one of the undead, playing on the guilt and fears of his family. To try and save the soul of the boy Gaspar, his grandfather, let the vampire child bite him all so he could get close enough to stake the lad. This killed Viktor but left Gasper infected. Instead of immediately being killed, though, Gaspar used this new connection to lead the team (well, what was left of them) to Dracula's lands so they could find where Illyana was being kept. Then Gaspr fully turned, with Pascha the one that had to kill him.
Dracula, meanwhile, played with his new toy, taunting Illyana before pouring some of his own blood into her mouth. Soon after, Christopher came into their secret alcove to see Illyana chained to the wall with Dracula looming over her. Hero and villain exchanged heated words before the vampire attacked, plunging them into a furious battle. As Dracula swooped around, with Christopher attacking with his whip, it was the master vampire that was defeated. Christopher freed his wife and their ragtag band went home, thinking themelves free of Dracula's curse.
Six months later, we find Illyana pregnant with Pascha living at the estate as Christopher and Illyana's ward, the Belmont lands once more a happy home. But, as we learn, Dracula's foul magic still hung over the couple as the baby within her had a dark connection to Dracula's magic, a connection that... well, would never be explained in the comics because a sequel was never produced.
Likely the demon-spawn baby was a reference to Soliel Belmont, son of Christopher, who is tempted to the darkness by Dracula around his fifteen birthday. How that would have played out in the comics is not known, sadly.
Playing as Christopher:
Christopher, in many ways, plays a lot like Simon. He has similar controls, a similar (although not exactly the same) upgrade system to his whip, the ability to use sub-weapons. He does, however, have a couple of tweaks to the formula that help to set him apart. Firstly, Chris doesn't have to worry about jumping onto and off of stairs -- neither Adventure game has any stairs at all. Instead, the levels are laid out with ropes and chains for the Belmont to climb, and he can freely jump onto and off of them.
And while his whip skills are similar to the NES version of Simon, Chris gets a special power on his second whip upgrade: the ability to shoot fireballs from his whip. The downside of this final upgrade was then, when Christopher takes damage, he loses the update and has to find it again (hidden in another candle). So while the fireball was very handy, it's use was very limited. It's worth noting that the fireball upgrade made an appearance in Castlevania: The Adventure ReBirth, but while Christopher could still lose the upgrade by being hit, it also had a time limit on it, so even if the player could avoid taking damage, the fireball would still run out over time.
One interesting fact that is worth mentioning is that, originally, Christopher Belmont and Trevor Belmont were meant to be the same character. That was the plan from Konami, naming the character Trevor C. Belmont (or Ralph C. Belmont, if you go with the original Japanese names), with the "C" standing for "Christopher". During the English translation for the Castlevania Adventure, the character was named Christopher and it stuck. Eventually the continuity was officially retconned to make the two heroes different characters on the timeline.