Short answers, pulled from the story.
Callimachus was an ancient Greek poet, scholar, and librarian born around 310 BC in Cyrene, a Greek city on the coast of modern-day Libya. He was active in Alexandria during the 3rd century BC and is believed to have died by 235 BC, at approximately 75 years of age.
The Pinakes was a comprehensive catalogue of all Greek literature compiled by Callimachus while he worked at the Library of Alexandria. It ran to 120 volumes, equivalent to five times the length of Homer's Iliad, and according to classicist Lionel Casson was the first comprehensive bibliographic resource for Greek literature.
Callimacheanism refers to Callimachus's aesthetic preference for small-scale, refined, recondite, and experimental poetry over the lengthy heroic epic that dominated his era. He summarized his approach in an allegory at the opening of the Aetia in which the god Apollo instructs the poet to keep his Muse slender and to tread an untrodden path.
Of more than 800 works attributed to Callimachus, only his Epigrams and six Hymns have been transmitted complete. The Aetia, the Iambs, and the Hecale survive in fragments, with their contents partly reconstructed from ancient summaries and references in classical literature.
Catullus, Horace, Vergil, Propertius, and Ovid named Callimachus among their principal models. Propertius called himself a "Roman Callimachus", while Ovid described Callimachus as "lacking in genius but strong in art", a formulation that acknowledges his emphasis on technical skill and erudition.
The Aetia is a collection of origin stories explaining contemporary phenomena through myths from the past. Estimated at around 4,000 lines organized into four books in elegiac couplets, it opens with a dream in which the young Callimachus is transported by the Muses to Mount Helicon to question them about the origins of unusual customs.