Fire Dragon/1.03

Fire Dragon are elite flyers.

The Fire Dragon is the standard for Dragons set way back in WBC1. Although not as terrifying as they were back then, they can still rip apart an enemy base with ease and are the main reason why you should never place buildings directly next to each other. Their trait of burning enemy infantry isn't particularly useful, but their main use is building bashing, where their fire attacks dispose of even the toughest of buildings rather quickly, as all buildings take +50% damage from fire attacks. Unfortunately for the Fire Dragon, WBC3 introduced the Swamp Dragon - a Dragon that is identical to the fire variant but with the added ability to erode armor. This does make the Fire Dragon obsolete for races that have access to both Dragons, such as Orcs and Ssrathi. A shame that an "acid" type was never introduced which could have widen the difference between the 2 Dragons.

Dark Dwarves
Fire Dragons follow the Dark Dwarven theme of specializing at tearing down buildings. The problem here is that Dark Dwarves have so many options at their disposal to do the job, that Fire Dragons aren't particularly needed. With Fire Bombs, Flame Cannons, Catapults, Battering Rams, Hellbores and even the Golems, there really is no need to spend such high resources on the Fire Dragon and you are better off going for the Frost Dragon in most cases. However, there is one thing the Fire Dragon can do that the many weapons-of-doom cannot - fly! This allows the Fire Dragon to attack an enemy from all directions and cause havoc when they least expect it, such as being used to sandwich an enemy base after once your siege weapons roll up and draw your enemy's attention, only for your Fire Dragon to strike from the complete opposite direction.

Benefits from Armorer and Mithril researches.

Daemons
Fire Dragons make for great building destroyers that surpass Salamanders for this act due to the absence of a piercing weakness that typical base defenses can pray up on. Being a flier only promotes this role further, especially in the Daemon race, where it can come from any angle and with a horde of powerful Daemon units that'll easily exploit any vulnerability found in the enemy's base defense. Between Imps, Succubi, Daemons, Harpies and even Firebats, there are a multitude of units that can accompany the Fire Dragon safely trough the hidden corners of an enemy base, causing utter havoc regardless of what defense the enemy has prepared.

Benefits from Daemonic Sight research.

Dwarves
Fire Dragons excel at tearing down buildings, but so do the Dwarven race as a whole. This means the Fire Dragon can't stand out from the race as a dedicated building demolisher, but instead used as addition base siege support. To make the most of the Fire Dragons from the Dwarven race, one should capitalise on their ability to fly and strike an enemy's base from positions that are difficult to defend (usually the back or by impassible terrain) and at the same time your Siege Weapons roll up at the front of their base, drawing attention away from the Dragon's attack.

Benefits from Armorer and Mithril researches.

Knights
The Fire Dragon is the most common and well known species of its kind. Fire Dragons cost a lot to produce and can only be accessed at a level 3 flier building, but they make up for it with splash damaging firebreath which alights any enemy within its attack.

Benefits from Crusade, Armorer, Order of the Rose, and Order of the Dragon researches.

Orcs
Orcs are, unfortunately, one of the 2 races in the game that gets both the Fire Dragon and Swamp Dragon. This effectively means Orcs only get one Dragon type, as the Swamp Dragon is identical to the Fire Dragon but with the added bonus of lowering enemy armor. Because of this there is simply no reason to build Fire Dragons when playing as Orcs.

Benefits from Training and Eagle Eye researches.

Ssrathi
The Ssrathi are, unfortunately, one of the 2 races in the game that gets both the Fire Dragon and Swamp Dragon. This effectively means the Ssrathi only get one Dragon type, as the Swamp Dragon is identical to the Fire Dragon but with the added bonus of lowering enemy armor. Because of this there is simply no reason to build Fire Dragons when playing as the Ssrathi.

Benefits from Eagle Eye research.

The Swarm
The Fire Dragon is not a bad unit by any means, but The Swarm would have killed for a different Dragon - one that doesn't use, yet again, a fire typed attack. With Scarabs, Fire Elementals and Scorpionpriests (and even Bone Catapults), The Swarm don't need another unit for razing buildings, which is the specialized role of the Fire Dragon. (Although, there isn't many Dragons that could fit in The Swarm's army - but I like to believe that there could always be a "Wind" Dragon out there, one that could represent the Desert Winds. Or perhaps the Scorpionpriest could summon Air Elementals with the same logic)

Benefits from Eagle Eye research.