There's a reason — or rather, there are innumerable reasons, in the form of paintings, sculptures, drawings, murals, pottery pieces and more — why Pablo Picasso is the most famous artist of the past 100 years. For well over seven decades, right up until his death in 1973 at the age of 91, he created thousands of works, many of them instantly recognizable masterpieces, in a dizzying array of media and in seemingly countless styles that he himself either pioneered or perfected.
Of course, scores of towering 20th-century artists (Matisse, O'Keeffe, de Kooning, Chagall and on and on) enjoyed prolific, long-lived careers. But Picasso really is the face of 20th century art, the archetypal, self-reinventing creative force whose most renowned works — Old Guitarist (1903), the gorgeous harlequin paintings of his Rose Period, Les Demoiselles d'Avignon (1907), Guernica (1937) — became defining, totemic emblems of the eras in which they were made.
Here, LIFE.com celebrates the Modernist master's career with a series of pictures by photographer Gjon Mili made over roughly two decades in the middle part of the last century. Mili, a daring technical innovator himself, first visited Picasso at Vallauris, in the South of France, in 1949. When the photographer showed the artist some pictures he'd made of ice skaters with tiny lights affixed to their skates, leaping in the dark, the Spanish genius was intrigued and lent his own special twist to a series of portraits made with the same general technique. (See slides 10, 11 and 12.)
"Picasso" LIFE magazine reported at the time, "gave Mili 15 minutes to try one experiment. He was so fascinated by the result that he posed for five sessions, projecting 30 drawings of centaurs, bulls, Greek profiles and his signature. Mili took his photographs in a darkened room, using two cameras, one for side view, another for front view. By leaving the shutters open, he caught the light streaks swirling through space."
Mili would revisit Picasso again through the years, each time encountering yet another side of the man while also documenting the artwork that seemed to pour forth in an unending torrent from Picasso's tireless imagaination.
In 1967, for example, Mili returned to the South of France, where Picasso was living, in Mougins, with his second wife, Jacqueline Roque. Inside the artist's workshop, he found a few small metal monkeys that Picasso had fashioned, seemingly on a whim (see slide #8). LIFE described Picasso's technique in creating these wonderful, playful sculptures: "He made paper cut-outs, then had the patterns transferred to sheet metal which he folded into animals with lively personalities, turning his paper-thin material into surprisingly substantial works of art."
Meeting Picasso could be an overwhelming experience, as LIFE's managing editor George P. Hunt wrote in a 1968 special issue of the magazine devoted entirely to the artist:
To see Picasso for the first time is to see, under that bald brow and pate, two extraordinary deep-brown eyes. They are strangely big for the face. And they change as you watch him talk and listen, so noticeably changing with the reflections of what passes through his mind, perhaps racing back into experience to enrich the present. They brood. They make mischief, they are friendly, offended, hostile, arrogant, bored, then suddenly interested. Mostly, during our visit, they laughed.
Like so many other artists, however, Picasso was hardly a saint. His long-time muse, Françoise Gilot (pictured in this gallery in slides 14 and 16), left Picasso in 1953, and in 1964 she wrote a tell-all memoir of their time together. With its less-than-flattering tales of his incessant affairs and titanic insecurities, her book so angered Picasso that he spitefully refused to see their children, Claude and Paloma, ever again. (By 1970, Gilot had married another world-famous genius: American virologist Jonas Salk, developer of the polio vaccine.)
While hardly providing an exhaustive portrait of one of the West's seminal creative figures, the pictures in this gallery nevertheless offer an inkling of Picasso's protean genius, and an intimate look at some of the places where that genius bore such singularly influential, and beautiful, fruit.
Ben Cosgrove is the editor of LIFE.com