Short answers, pulled from the story.
Greek fire is attributed by the chronicler Theophanes the Confessor to Kallinikos, a Jewish architect from Heliopolis in Syria, who fled to Constantinople around 672. The historian James Partington considered it more likely the weapon was developed collectively by chemists in Constantinople building on the Alexandrian chemical tradition, rather than by a single inventor.
The exact formula was never recorded and remains unknown. Most modern scholars agree it was based on petroleum, comparable in composition to napalm, likely thickened with resins to increase burning intensity. A ninth-century Latin manuscript preserved at Wolfenbüttel identifies naphtha as the main component.
The primary method was a bronze tube called a siphōn, mounted on the prow of a warship, which projected the heated and pressurized liquid and ignited it at the nozzle's mouth. Portable hand-held versions called cheirosiphōnes were also used on land and at sea, and earthenware grenades filled with the substance were thrown by catapult.
Knowledge of the weapon system was deliberately compartmentalised, with each operator or technician knowing only one component. When the Bulgarians captured 36 projecting tubes and quantities of the substance itself in 814, they still could not make use of them. The complete formula, manufacturing process, and deployment system all had to work together, and no enemy ever obtained all of it.
Greek fire continued to be mentioned in Byzantine sources through the twelfth century, with Anna Komnene describing its use against the Pisans in 1099. By the 1203 siege of Constantinople, no account confirms its use, possibly because the empire had lost access to its primary ingredients or because the secret had been lost.
Naval historian John Pryor noted it was not a "ship-killer" comparable to the naval ram, and its siphōn-deployed version had limited range and required calm water and favorable winds. Despite those limits, historian John Julius Norwich wrote that it is impossible to exaggerate its importance in Byzantine history, pointing to its role in repelling the Arab sieges of Constantinople.