His studios were crammed with sketches and outlines of countless portraits. The famous painter preferred to work with models who would be around for the entire day, like family members, wives and children. Sitting still for Picasso was part of the normal daily routine.

Picasso met Jacqueline Roque in 1952 at the Madoura pottery workshop where his ceramics were baked. When Picasso married her in 1961, he was already 80 years old, and she was 34. She helped him in his work while protecting him against the outside world, remaining his companion, muse and model until his death in 1973. He created over 400 portraits of her.

One of his muses was 19-year-old Sylvette David from England, whom Picasso had met in 1954. Totally enraptured by the young blonde woman, he produced 50 drawings, paintings and sculptures of her within one month only. Her trademark ponytail became trendy in the 1950s.

Picasso's friends also appear in his oeuvre, including painter Amadeo Modigliani (left, with Picasso, center, and art critic André Salmon, right). This picture was taken by Jean Cocteau in 1916 in front of their favorite coffee shop in Paris, Café de la Rotonde. Cocteau was also portrayed several times by Picasso.

Throughout his life, Pablo Picasso developed close friendships with his art dealers, especially Daniel-Henry Kahnweiler. In 1907, the German-French art historian opened a small Gallery in Paris, signing exclusive contracts with artists who were to become famous later on - among them Picasso. In 1910, he painted this Cubist portrait of Kahnweiler.

The interior world of his studio fully sufficed for an obsessed artist like Picasso. Simple vases, bowls or the bust of a woman served as models for sketches or a huge oil painting. As a painter and drawer, he remained faithful to his themes for a long time as they repeatedly popped up in different versions in his works.

In spite of all his hard work, Picasso did find time for humor, producing cartoons just for fun. In this case, he embellished a pin-up picture out of a film magazine of Esther Williams with a portrait sketch of his artist friend Juame Sabartés. The Hollywood actress became famous for swimming scenes in her films. Among her admirers was also Picasso.

Following numerous love affairs, the young painter met Russian ballerina Olga Khokhlova in 1917, and married her. She voluntarily gave up her career at the world famous "Ballets Russes" - and facilitated his access to exclusive Paris circles. The Picasso exhibition at London's National Portrait Gallery, held until February 5, 2017, devotes an entire room to portraits of her.

"I have not painted the war, because I am not the kind of painter who goes out like a photographer looking for something to depict. But I have no doubt that the war is in these paintings I have done," Spanish painter Pablo Picasso said after the end of WWII. From 1939-1945, Picasso primarily painted portraits, nudes or still lifes such as "Three Lamb's Heads" (1939), which had dark undertones.

In June 1940 the Nazis occupied Paris. Picasso, who had called the city his home since 1904, had fled to southern France when war broke out. But in August 1940 he returned to his Parisian studio, despite the occupation. The Nazis termed him "degenerate" and prevented him from exhibiting his art. Yet Picasso remained in his adopted homeland until the war's end, unlike many of his colleagues.

Picasso, a Spanish citizen, had applied for French citizenship in early 1940, but his application was rejected because of his supposedly extremist communist tendencies. Unable to show in Paris, the artist was celebrated in New York. In 1939-40 the Museum of Modern Art hosted a retrospective of his major works, including "Guernica," the stark mourning tribute to the Spanish Civil War (1936-39).

Before World War II, the Spanish artist had taken a clear political stance. He even mocked dictator Francisco Franco, portraying him as the hapless Don Quixote. He donated proceeds from published works to Spanish refugee aid organizations and gave the profits from exhibitions to Spain's republican party. Yet his works during WWII, including this dove from 1942, appeared harmless in comparison.

"Why do you think I date everything I make? Because it's not enough to know an artist's works. One must also know when he made them, why, how, under what circumstances," Picasso explained in 1943. "Still Life with Skull of Ox" was created one year earlier. Skulls, often a symbol of the fragility of life, are a frequently recurring motif in his work during the WWII years.

In 1944 the Allies liberated Paris. Picasso was celebrated as a survivor. He joined the Communist Party but was accused by some of his comrades of having been too apolitical artistically. He replied that the artist "is a political being, constantly aware of the heart-breaking, passionate, or delightful things that happen in the world, shaping himself completely in their image."

Picasso frequently traveled to the South of France after WWII. In 1945 his style changed again, and he began to reinterpret works by the old masters. The artist remained politically active, taking part in world peace congresses, among other events. During this time, he also created his drawing of a dove of peace, which remains an internationally recognized symbol to this day.

"Pablo Picasso: The War Years 1939-1945" shows Picasso's life during a challenging period of threats and destruction. The exhibition runs from February 15 to June 14 at the K20 exhibition space in Dusseldorf, part of the Kunstsammlung Nordrhein-Westfalen, in Germany's northwest. The show is a collaboration with the Museum of Grenoble and the Picasso Museum in Paris.