Fire-type, is one of the original 15 elemental types of Pokémon. It is also one of the original six types in the TCG. It is one of the most notorious types that is part of not one major trio, the starters-dominated Fire-Grass-Water trio, it is also part of the primary elemental Fire-Ice-Electric and its cousin, the Fire-Water-Electric trio. Fire is also one of the few types that have a dedicated evolution stone to it, Fire Stone, and a weather dedicated to it, Sunny Day.
But the fun doesn't stop there. Fire-types houses the second highest BST starters have, 534, which is shared by 4 of the seven Fire-types introduced in the metagame. It also houses three Mega Evolutions for the said starters, with one particularly infamous one, Charizard, the mascot of the original Red game, getting two Megas.
To put it bluntly, Fire-type is a pretty big deal. But how it became such a big deal? Well, to start off, almost every RPG franchise has some sort of Fire element, based off one of the four main elements. More specifically though the idea of fire captivated the human imagination as the primary vessel of the technological change, so it is not surprising that hot blooded seven year old Japanese kids would be attracted to it. But we will be discussing the overall evolution of the type within the context of the franchise.
The History of Fire-type in Pokémon:
The Fire-type started off as one of the earliest types you can get, as one of your starters, Charmander, was one of these fateful kindlers. In this era to third generation, Fire-type would be remembered as a Special-type, meaning that Pokémon would attack and defend this type with their Special stat. This type based matchup helped determine some of the statistical archetypes that would define the future Pokémon. In this game, Fire-type was the last of the starter types you would face, in the Cinnabar Island. This little Island also housed the primary Fire-type domain, the Pokémon Mansion, a burned down mansion full of after-burning thieves, that served the primary Fire-type NPC archetype.
The next game Fire-type would see a mascot for was Gold. This game featured the first major change in the stats of Pokémon with the Special split, where Special stat split into different stats. The vast majority of Fire-types gained their Special as their Special Attack, while their Special Defense was given as a weaker stat. This sealed Fire-type's fate as a strong Special offensive type. Most notably however, this generation introduced two major things. One was Sunny Day, the weather for Fire-types, which reduced their Water weakness while improving their Fire moves, and making Solar Beam last one turn. The second one was introduction of Fire Punch as a TM, for bipedal Special Attack users that needed it.
The third generation would feature a mascot that was a Fire-type all but in name, Groudon, and a team dedicated to Fire-type all but in name, Team Magma. Both of these provided several strong moves like Heat Wave, a staple for Doubles, Eruption, the original signature move for Groudon(though it was obtained by other Pokémon), Overheat, a powerful TM, and Will-O-Wisp, a burning status move that served as the Toxic for Fire-types. This generation also effectively reintroduced Sunny Day with Groudon, whose ability Drought summoned the weather permanently upon switching in. This generation also expanded on Solar Beam and gave it to plenty of fully evolved Fire-types, and introduced Abilities, most relevant ones being White Smoke, a former signature Ability for Torkoal, Flash Fire, which granted immunity to Fire, Magma Armor, which granted immunity to freezing, and Flame Body, which caused burn upon contact. The last two would gain outside of battle effect for halving the Egg Steps necessary for hatching a Pokémon Egg.
The fourth generation was something that could be considered as a Fire-type Winter. Only introducing two new Fire-type lines, one being the starter, the other being a post-game Legendary and a third cross-generational evolution that is only available post-game, this generation has introduced no Fire-types that can be obtained in the wild conventionally. Instead, it reused an old mid-game Fire-type, Ponyta-line, as its early Fire-type, and only Fire-type. Though this was somewhat fixed in Platinum, which also reintroduced Houndour-line, Magby-line and Flareon, this remained a controversial choice. The other major change happened in HGSS, the remakes of Generation II games, which made their regional Fire-types actually available pre-E4, after they were made available in Hoenn and Sinnoh respectively. Another controversial choice was the introduction of Stealth Rock, a Rock-type entry hazard that caused damage based on type effectiveness, up to %50 for Pokémon that were weak to Rock *4 times. This heavily nerfed Fire-types from the competitive metagame, making the franchise staple Charizard and its Gen I allies complete jokes, and further hampered the two defensive Fire-types, Magcargo and Torkoal.
In addition to this, the Physical/Special split was introduced, which changed the type dynamics completely. Many bipedal Special users who used Elemental Punches were made irrelevant, while Fighting-types thrived. To compensate for this, the few Physical oriented Fire-types were given Fire Fang and Flare Blitz, one being a Fire-type version of Bite, other being a Fire-type version of Double-Edge. In addition to this, Heat Wave was made a Move Tutor, which gave Flying-types a completely new coverage move and relevance in Sun teams.
Most notorious event was the introduction of Drought to a non-Legendary Pokémon, Ninetales. With permanent weather still in effect, this caused the phenomenon that was called the "Weather Wars", where every competitive team was centered around a weather and preserving it for the rest of the battle. The weather abilities were nerfed the next gen, which made them just summon the standard 5-turn(8-turns if holding the respective rock), and pushed back Weathers to irrelevancy.
Interestingly, this generation remains as the only generation to not have a Fire-type Legendary if we include Primal Groudon's posthumous introduction, though since Silvally is counted as a Legendary by TPCi, that is probably not entirely correct.
The Overview of Fire-types:
Of all the three major starters, Fire-type is the one that is geared towards offense, and generally dual offense. The few defensively oriented ones are generally oriented towards Physical Defense rather than Special Defense. This is because of the effect of Special split, which made the majority of Fire-types Special Offense oriented. However, another reason comes from the effect of Burn, which halves the Attack of the opponent. This leaves Fire-types very open to Special attacks, generally Water-type moves. Similarly, there are almost no Fire-types with high HP stats.
Fire-types can also be very slow, due to the focus on offense, and the nature of fire. Flame Charge helps, but it is not a saviour. Neither is Trick Room. This, combined with their many weaknesses makes them easy to defeat, especially since their weaknesses are to common offensive types like Rock, Water, Ground.
Because they are so heavily offense oriented, there aren't many Fire-type status moves, besides the aforementioned Sunny Day and Will-O-Wisp. However, both of those moves are available to variety of different Pokémon, so while they are a godsend for Fire-types, they do not make Fire-types relevant in comparison to other options.
Fire-types also do not have a stat raising move of their own, instead they use other moves like Work Up, Bulk Up, Dragon Dance, Calm Mind etc. It is hard to say what would be a Fire-type stat raising move(maybe a Special Hone Claws) but that causes greater disunity in Fire-types.