Charizard in depth
Rizādon, or the lizard that stopped just short of being a dragon
The design was done by Atsuko Nishida, and the line was drawn backwards from the way it's played: first the large creature, then working back from there until reaching the small lizard handed over by the professor. The Japanese name, リザードン (Rizādon), combines the pronunciation of lizard with -don, the ending carried by dinosaur names that also hints at “dragon.” The English name, Charizard, combines char—to scorch—with lizard, and Spanish left it unchanged.
What it didn't keep was the type. Everything about the creature points to Dragon: the wings, the neck, the horns, even the name's ending. And yet it's Fire and Flying, with the practical result that a Rock move deals four times the damage instead of twice as much. That's the difference between entering a field with Stealth Rock up and not being able to do it.
Three bodies for the same number
Of all the alternate forms it has had, the one that corrects the slight is Mega Charizard X: it becomes Fire and Dragon, with Tough Claws strengthening physical contact moves, which fits Dragon Claw and Flare Blitz better than the base version. Mega Charizard Y takes the other route and stays Fire and Flying, but brings Drought, so it sets up its own sun on entry and stops depending on someone else to do it—with Solar Power in the background, the reading is obvious. The Gigantamax form, from Sword and Shield, is the third: same Pokédex number, three different silhouettes.
When each thing arrives
In a normal playthrough, the problem isn't power, it's timing. Air Slash appears upon evolving, and Heat Wave and Dragon Claw can be recovered from the level 1 list at the Move Reminder. After that, things spread out: Fire Fang at 19, Slash at 24, Flamethrower at 30, then a jump all the way to Inferno at 54 and Flare Blitz at 62, which arrives after the League has already been beaten. Dragon Breath at 12 and Fire Spin at 46, with 35 power, are filler.
The underlying mismatch is that half of what it learns by level is physical—Scratch, Fire Fang, Slash, Flare Blitz—while its Special Attack is twenty-five points higher than its physical Attack. Anyone who doesn't want to fight that stays with Flamethrower and Air Slash and leaves everything else alone.
Who not to bring it out against
The obvious comparison is Dragonite: the same big-dragon feel, the same weakness to Ice, but with the type Charizard was denied and without the quadruple weakness to Rock. In a mountain full of Rock types—its own habitat, incidentally—that 78 Defense shows immediately. Against Water types, there's no story either: Hurricane and Fire Blast fall short, while Solar Beam, which is in its TM list with 120 power, needs sun or a turn to charge.
Outside the mainline games, the species has been the face of the Pokémon Red and Pokémon FireRed boxes, which explains why it was given three alternate forms when most of the Pokédex hasn't been given any.