When you have a game about a child-like Dracula (who is usually attributed as actually being Alucard by Konami, even though he calls himself "Kid Dracula" in the game) adventuring the world as a kind of "hero", you have to have a villain. The character that would normally be the villain, Dracula, is used in a different role, so what do you do? Konami's answer this in their (Japan-exclusive) parody spin-off, I'm Kid Dracula, was to create a new villain, one nevre seen before, to act as a foil to Dracula less-than-dasterdly plans.
For whatever reason, Konami decided that a giant lizard-king was the best for for Dracula (Alucard) to fight. This beast, Galamoth, was creadited as being just a big a villain as Dracula so Alucard had to take the lizard king out. It's a silly plot for a silly game, which is why it works. The game was successful enough to generate a sequel, so naturally Galamoth came back as the villain for a second time.
That would have probably been the end of his story if not for a little game called Castlevania: Symphony of the Night. An adventure starring a grown up Alucard, series producer decided to throw a little nod towards the classic Kid Dracul games in, and included a version of Galamoth in as a special boss fight late in the game. From end boss of two titles to a minion within Dracula's castle, plainly Galamoth had fallen on hard times.
Since he'd already shown up in the main series, it made sense to bring the lizard king back for one last go round near the end of the main series (at least under IGA's tenure). With the fighting game Castlevania: Judgment the decision was made to make Dracula a playable fighter. Thus, a different villain would be needed, and who better than Galamoth himself?
For a joke that played off a joke that appered in a parody game, Galamoth has actually had quite the long and illustrious tenure, showing up in more games than many of the other "main" villains of the series.
Kid Dracula History:
Demon Castle Special: I'm Kid Dracula
On planet Earth there was room for only one true villain. For years, decades even, that villain was Dracula, who commanded a legion of the undead so great no one else could stop him. However, while Dracula was detained with pressing business, his son, also named Dracula, was left in charge of the castle. Unfortunately for kid Dracula, that was when Galamoth decided to strike. A lizard king from another dimension (who was, at times, acknowledged as a god in this world, such as during the time of Ancient Egypt), Galamoth used the temporary lapse in power of Dracula's empire to strike, stealing away Dracula's army and claiming the title of biggest villain for himself.
For the kid Dracula, this slight against his father simply could not stand. Taking this as a clue to get out of the castle and explore the world, the young Dracula knew he had to face off against Galamoth both to reclaim his father's power and, in the process, make his own statement about who the biggest bad ass in the world was (in short: Kid Dracula). Thus, venturing out, the young Dracula took on the various traps and damgers Galamoth laid out for him, through forests and mountains to the Galamoth's own fortress.
Within this great castle, the young vampire faced off against the lizard king in combat. The fight was intense, but the youthful Dracula came out the victor. Galamoth was banished back to his own dimension while Kid Dracula went hom a victor and rightful claimant to the evil power of the land (at least until his father returned).
Galamoth, though, would not take this defeat so lightly. A year later, sensing that the elder Dracula still hadn't returned to claim his power, Galamoth once again launched his attack at the seat of evil power. He again stole away Dracula's minions, claiming the title of biggest villain for his scaly self. He also challenged the younger Dracula to a rematch, calling him out as "not the biggest villain".
Well this Kid Dracula just could not let stand. Taking up his cape once more, the younger vampire again ventured out to face the many traps and dangers Galamoth has set before him. Again the adventure was arduous, but the vampire lad took every challenge on, defeating them all in kind.
At the last fortress, the young Dracula again faced off against Galamoth in a battle of strength and wills. Although the two fought viciously, it was the young Dracula that came out the victor once more. He returned home to the cheers and adulation of his people while Galamoth was kicked to the curb, banished to his own dimension to plot and scheme once more.
Castlevania: Symphony of the Night
Years later, during the events of Symphony of the Night, Galamoth once again returns to Dracula's castle. His plan was to once again take control of Dracula's power (and the throne of the Netherworld, the land where Dracula's castle, and minions, reside when not summoned by Dracula).
This time, however, Dracula and his minions were ready. When Galamoth intruded into the realm of Earth, Dracula's minions captured him and enslaved the Lizard King in the deepest catacombs of the Inverted Castle. Here, Galamoth was forced to wait, unable to escape, hoping to use some distraction to plot his vengeance. Plot he did, and a possible distraction did arrive in the form of Alucard, who was at the castle on his own mission.
Unfortunately, much like in the previous encounters he had with the vampire lord's son, the battle between vampire and lizard king went very poorly for Galamoth. Instead of killing Alucard and freeing himself from the prison, Galamoth was defeated and banished once more, forced to reside in his home dimension until his powers had built up again.
As an interesting note, Galamoth's description in the game states that he has a "10,000 year plan to claim the throne of the Netherworld". THis lines up, in a way, with the age given for Kid Dracula in the parody games, where the young "hero" is listed as 10,009 years old. Obviously, for the sake of actual Castlevania continuity, that age is completely ludicrous. It is interesting to note it, though, as it does roughtly line up, too, with the time of the later game, Judgment which takes place in 12,000 AD, or roughtly 10,000 years after most of the games in the series.
Centuries after his last attempt at the throne of the Netherworld, Galamoth make one last-ditch effort to claim the power for himself. Reasoning that Alucard has always been there to stop him and, when not Alucard, Dracula himself has had enough power to thwart the Lizard King, the best course of action would have been to simply remove Dracula from the timeline. Calling upon the Time Reaper, a version of Death from the future, Galamoth send the reaper to eliminated Dracula's era of power, simply wiping him and all his people from existence.
However, Galamonth didn't count on an agent of time, Aeon, stepping in to save the time line. Gathering the best and most powerful warriors from across the timeline, Aeon put his warriors of light and darkness into a competition in a time rift all to find the one capable of facing off against the Time Reaper. These warriors fought fiercely and, in the end, joined forces to send the future Death back from whence he came, his mission unfulfilled. They were then sent back to their own timelines while Galamoth was once again forced to wait, alone, in his home dimension.
Although not an official appearance of the character, Galamoth's soul shows up in Castlevania: Aria of Sorrow, granting Soma Cruz the ability to "see past areas blocked by time" (specifically the section blocked by the Chronomage enemy), which Soma gains after defeating Legion.
And while Galamoth is name-checked in Judgment, he doesn't officially appear in the game. He sets the plot in motion, but it's the Time Reaper who actually does the dirty work.
Fighting Against Galamoth:
The fight with Galamoth in the first Kid Dracula game actually takes a couple of forms. The first fight is against his regular form (sometimes called "Galamoth Jr."), where the Lizard King with run back and forth, using a sword to block shots while occasionally breathing fire and slashing his sword. The top of his head is his weak points, so you'll need to layer on the shots while dodging his telegraphed atakcs to win this round.
After this, the next full encounter is with Galamoth's larger form. Here, the lizard will warp in and then fly along the top of the screen, regularly shooting down beams of lightning that you'll have to stand between both to avoid getting him and so you can shoot upwards and hit him in his vulnerables (his open mouth). He'll eventually also shoot at you from his mouth, so be ready to dodge out when this happens. The battle can take a little while, but it's really pretty short in comparison to some of the fights. Just avoiding the damage, and not trying to get in more shots than necessary, can be the hardest part.
For the Game Boy sequel, there are again two fights with the various forms of Galamoth. The smaller form (Galamoth Jr. aka Robo Galamoth) resides at the top of a tower into space that you'll have to scale before you even get to the main fight. Once at the top, you'll have to shoot at flying sacuers (and the aliens they drop), killing enough of these to make Galamoth Jr. spawn in. His fight is a lot like the battle in the first game: he'll shot at you with his sword causing a laser beam to go across the creen (like his fire breath in the first game). You'll have to layers shots in to the top of his head while avoiding the sword itself as that will block your shots. Also watch out for the beast himself as he's fairly agile and will jump back and forth across the screen. Layer on the damage to quickly kill the beast.
The fight isn't over yet, though, as once you defeat the first part, the robot's head will get blown off. It will continue to pace back and forth, jumping too, while occasionally one of the aliens will stick his head out -- you have to shoot the alien as that's the only vulnerable part during this fight. Occaisonally, too, the alien will throw out bombs that explode once they hit the ground. He's very pattern based and easy to dodge, but due to his limited vulnerability window this fight can take a while to complete.
Galamoth's last appearance in the Kid Dracula games is in a fight with him as the last boss for the sequel. Like with the Galamoth Jr. fight, this battle starts the same as in the last game. Galamoth will fly over head, shooting down lightning that you'll have to stand between to avoid (and get in a shot when ready). He'll also shoot angled bursts of lightning you'll need to avoid. Eventually he'll open his mouth and you an try to layer in shots while dodging hte fireball hs spits out.
Once you defeat this first phase, Galamoth will lose his wings and drop to the ground. From here, he'll bounce back and forth attempting to land on you. He's still only weak when his mouth is open so you'll have to wait until he's overhead, mouth open, and shoot upwards to land in damage. This can take a while as he doesn't open his mouth often and it can be difficult to land shots in the small target window. Take your time and be careful and you'll come out the victor (eventually).
Moving into the main Castlevania series, Garamoth's sole appearance in Symphony of the Night can be pretty tough if you don't have the right equipment to handle all his lightning damage and enough levels to soak the damage at times. Using his scepter, the hulking beats will stand at the right edge of the screen and cast either orbs of darkness or a lightning storm down on the hero. The best way to defeat him is to go for his feet and either absorb/soak the lightning damage (the right circlet, when equipped, will actually heal you from lightning) or change to mist form when the summons the storm. Stand at the right spot and you can attack his foot without getting damaged yourself. Just dont stand too close and, when he brings out the foot, he'll kick you back, causing you massive damage.