Short answers, pulled from the story.
Berlioz is best known for the Symphonie fantastique (1830), a purely orchestral work that introduced the concept of the idee fixe, a recurring melodic theme representing an obsession. He is also celebrated for Les Troyens, a five-act opera based on Virgil's Aeneid, and for his Treatise on Instrumentation (1844), which remained a standard reference well into the 20th century.
Harriet Smithson was an Irish Shakespearean actress whom Berlioz first saw performing in Paris in 1827. He pursued her obsessively for years before she accepted him, and they were married at the British Embassy in Paris on the 3rd of October 1833. The idee fixe theme running through the Symphonie fantastique was Berlioz's idealised portrait of her.
The Prix de Rome was France's premier music prize, awarding winners a two-year residency at the Villa Medici in Rome. Berlioz made four attempts to win it. He succeeded in 1830 with the cantata La Mort de Sardanapale, deliberately moderating his natural style to satisfy the conservative judges after his previous entry, Cléopâtre, was rejected for what they called dangerous tendencies.
Les Troyens is a five-act, five-hour opera that Berlioz completed in 1858, but its scale made it unacceptable to the management of the Paris Opera. The only staging he achieved was a truncated version of the final three acts at the Theatre-Lyrique in November 1863, during which further cuts were made across a run of 22 performances. A complete, uncut staging in French did not take place until 1969 at Covent Garden, marking the centenary of his death.
Berlioz introduced instruments previously reserved for special effects into the regular orchestra, including the harp, cor anglais, bass clarinet, and valve trumpet. Richard Strauss, who was commissioned to revise Berlioz's Treatise on Instrumentation in 1905, wrote that Berlioz invented the modern orchestra, and he left Berlioz's original text unchanged when he updated the book.
The rehabilitation began in earnest after the Second World War, when the introduction of the LP record made Berlioz's music widely available for the first time. In 1957 a professional company staged the complete original Trojans for the first time, at the Royal Opera House, Covent Garden. By the 1960s David Cairns considered Berlioz's greatness firmly established, and the critical consensus that had dismissed his harmonic procedures as clumsy was widely seen as obsolete.