Short answers, pulled from the story.
Mozart wrote Piano Concerto No. 9 in E major, K. 271, for Victoire Jenamy (1749-1812), a French virtuoso pianist and the daughter of dancer Jean-Georges Noverre. Mozart became acquainted with her playing when she performed in Salzburg in December 1776.
The Jeunehomme nickname came from scholars Théodore de Wyzéwa and Georges de Saint-Foix, who mistakenly attributed the concerto to an unnamed French pianist called Jeunehomme. Michael Lorenz corrected the record in 2004, identifying the true dedicatee as Victoire Jenamy. The confusion arose partly because Wyzéwa and Saint-Foix had to rely on error-prone transcriptions of Mozart's letters after being denied access to the originals.
Mozart completed the concerto in January 1777 in Salzburg, when he was 21 years old. He had finished his previous Piano Concerto No. 8 in C major about nine months earlier, with few significant works composed in the intervening period.
The first movement opens with immediate interventions by the soloist, which was highly unconventional in 1777 and anticipates the approach Beethoven later used in his Fourth and Fifth Concertos. The work also interrupts its rondo finale with a slow minuet section in A major, a structural procedure Mozart repeated in only one other concerto.
Charles Rosen called it perhaps the first unequivocal masterpiece of the classical style, Alfred Brendel described it as one of the greatest wonders of the world, and Alfred Einstein dubbed it Mozart's Eroica. Scholar Simon P. Keefe credited it with a depth of expression and a level of exuberant virtuosity that surpasses anything in Mozart's preceding piano concertos.
Only five of Mozart's piano concertos place the second movement in a minor key: K. 41, K. 271, K. 456, K. 482, and K. 488. K. 41 is an arrangement rather than an original composition, making Piano Concerto No. 9 (K. 271) one of a very small group of original works with this characteristic.