I didn't either until I saw some of his early paintings and learned he was a brilliant classical painter from a very young age (eg. "Portrait of aunt Pepa", at 14). The later surrealism and abstraction weren't due to a lack of technical skill, but his deliberate choice to create a new visual language that would reflect the rapidly changing world around him.

That shift also reflected the era he lived in - one where visual arts played a central role in the cultural conversation - making him a true part of the zeitgeist that is hard to imagine now when visual art feels less central and more inward-looking.

A lot of what feels cliche now started with him, it only feels commonplace now as his influence was so massive.

Imagine being born in 1850 when everyone got around on horseback and paintings were realistic portrayals of people, landscapes, religious figures in muted tones. Impressionism (Van Gogh etc) arrives and is considered radical, then in 1907 you see _Les Demoiselles d'Avignon_ with its bright colors and abstract depiction of cavorting prostitutes. It would certainly provoke a reaction. The 20th Century had arrived.

Picasso was an artistic prodigy from an early age, and was talented at painting in the styles of the day like realism etc.

The reason why he is influential and not forgotten is that he took painting in an entirely new direction and was able to convey emotion and philosophical ideas (like in Guernica, for example) in a completely different way than what was typical at the time. In a lot of his work he strips things down and distorts them on purpose to show multiple perspectives, which isn't something that realism usually tries to do.