Apollinaire, 1902, Cologne
Wilhelm Albert Włodzimierz Apolinary Kostrowicki was born in Rome, Italy, and was raised speaking French, Italian, and
 He emigrated to France in his late teens and adopted the name Guillaume Apollinaire. His mother, born Angelika Kostrowicka, was a Polish noblewoman born near
Grodno Governorate (present-day
Belarus). His maternal grandfather was a general in the
Russian Imperial Army who was killed in the
Crimean War. Apollinaire's father is unknown but may have been Francesco Costantino Camillo Flugi d'Aspermont (born 1835), a
Graubünden aristocrat who disappeared early from Apollinaire's life. Francesco Flugi von Aspermont was a nephew of Conradin Flugi d'Aspermont (1787–1874), a poet who wrote in ladin putèr (an official language dialect of Switzerland spoken in Engiadina ota), and perhaps also of the Minnesänger Oswald von Wolkenstein (born c. 1377, died 2 August 1445; see Les ancêtres Grisons du poète Guillaume Apollinaire at Généanet).
Apollinaire eventually moved from Rome to Paris
 and became one of the most popular members of the artistic community of Paris (both in
Montparnasse). His friends and collaborators in that period included
Marcel Duchamp and
Jean Metzinger. He became romantically involved with
Marie Laurencin, who is often identified as his muse.
In late 1909 or early 1910, Metzinger painted a Cubist portrait of Apollinaire. In his Vie anecdotique (16 October 1911), the poet proudly writes: "I am honoured to be the first model of a Cubist painter, Jean Metzinger, for a portrait exhibited in 1910 at the Salon des Indépendants." It was not only the first Cubist portrait, according to Apollinaire, but it was also the first great portrait of the poet exhibited in public, prior to others by
Pablo Picasso and
"La Joconde est Retrouvée" (The Mona Lisa is Found), Le Petit Parisien
, No. 13559, 13 December 1913
In 1911 he joined the Puteaux Group, a branch of the Cubist movement soon to be known as the
Section d'Or. The opening address of the 1912 Salon de la Section d'Or—the most important pre-World War I Cubist exhibition—was given by Apollinaire.
On 7 September 1911, police arrested and jailed him on suspicion of aiding and abetting the theft of the
Mona Lisa and a number of Egyptian statuettes from the
 but released him a week later. The theft of the statues was committed by a former secretary of Apollinaire's, Honoré Joseph Géry Pieret, who had returned one of the stolen statues to the French newspaper the Paris-Journal. Apollinaire implicated his friend
Pablo Picasso, who was also brought in for questioning in the theft of the Mona Lisa, but he was also exonerated.
 The theft of the
Mona Lisa was perpetrated by
Vincenzo Peruggia, an Italian house painter who acted alone and was only caught two years later when he tried to sell the painting in Florence.
Apollinaire was active as a journalist and art critic for Le Matin, Intransigeant, and Paris Journal. He once called for the Louvre to be burnt down.