Picasso was without serious question the most important painter of the twentieth century, and one of the key visual artists of any period. Just in case you're wondering what all the fuss is about, here's an incredible chronological record of Picasso's work. The main page takes a while to load, even with a fast connection, because it contains thumbnails of one painting for every year from 1889 (an amazing painting of a boy on a donkey done by the then eight-year-old prodigy) to 1973, the year Picasso died. What's more, click on any painting (1907's seminal Les Demoiselles D'Avignon, for instance), and up pops another page with, in this case, twenty-six more paintings from 1907. Click on the year instead of the painting and you get a very detailed biographical account of what was going on in that year.
It's an exhaustive and valuable archive; the man generated an awful lot of extraordinary work, and we're blessed to be able to peruse most of it online.
[Thanks to Grow-a-Brain for the link.]