Short answers, pulled from the story.
The Old French term dague referred to cross-hilt knives in the 13th century, alongside poignal and basilard. Middle English adopted dagger from the 1380s onward. The German equivalents dolch and degen appeared in the same Late Medieval period.
The dagger had an iron blade at a time when iron production had not yet begun in Egypt, making the material extremely rare. In June 2016, x-ray fluorescence spectrometry confirmed the blade was of meteoritic origin, matching the proportions of iron, 10% nickel, and 0.6% cobalt found in a nearby meteorite deposited by an ancient meteor shower.
The Fairbairn-Sykes fighting knife was developed by William E. Fairbairn and Eric A. Sykes, drawing on close-combat experience they gained while serving on the Shanghai Municipal Police Force. British commando and other elite units were issued the blade during the Second World War, using it primarily for sentry elimination.
At Agincourt in 1415, archers used daggers to finish off dismounted knights by thrusting the narrow blades through helmet vents and other openings in armor. The dagger's slender point made it effective against heavy plate and chain mail where cutting weapons were not.
The pugio was a double-edged iron thrusting dagger issued to Roman legionaries, its name derived from the Latin pugno, meaning "fight". Its design was taken directly from Iberian daggers and short swords, including the triangular-bladed form the Romans called the parazonium. It served as a soldier's last resort in close-quarter combat and as a utility knife between battles.
Under the Fascist dictatorships of Mussolini's Italy and Hitler's Germany, daggers became prominent ornamental uniform regalia. Other nations including Japan also used dress daggers, though never to the same extent as those two regimes.