The unknown dude sometime around 2000-1500 BCE who discovered you could get iron from ore?
But yes, the leap from copper/bronze (which could be discovered by simply dropping rocks into a fire, since copper melts at low enough temperatures) vs iron, which is a process that requires much hotter temperatures + forging techniques, is huge.
Learning to mix metals into alloys would eventually lead to the discovery of steel (mix iron + wood). Not as good as modern steel, but trial-and-error would get a process down over the centuries for sure.
The "Iron Forge" seems to be the hardest step in the whole tech tree. Its a huge leap, no matter how I think about it. Maybe some old pre-history metallurgist was lucky enough to play with meteorite-iron and noticed similarities to ore somewhere else.
Iron, as known to the ancients, was in many ways inferior to bronze. Iron with low carbon content is malleable but soft, whereas iron with too much carbon is hard but brittle. It took a long time for people to painstakingly learn to make iron that was consistently as good as bronze, and even longer to learn how to further refine iron into consistent-quality steel, a process that also required huge amounts of energy compared to bronzemaking.
No, this unknown dude was far later somewhere in Japan.[0]
Here's one I picked at random to get you started on catching up: