Iron is one of the most useful items in-game, as it creates tools that are capable of mining all ores and anything but obsidian (which can only be mined with a diamondpickaxe) and bedrock. It also creates the third strongest armor, with netherite being the strongest. This makes it perhaps one of the most-used materials in Minecraft.
Iron is used in the most amount of crafting recipes which are about 29 total.
Iron is also incredibly versatile. It fills all 3 categories where it is efficient in building, attacking and mining.
Because it's a rare drop by zombies, iron ingots are considered a renewable resource.
Weaponsmith, armorer, and toolsmith villagers will buy iron ingots in exchange for emeralds.