Short answers, pulled from the story.
Glycolysis consists of exactly ten reactions, each catalyzed by a specific enzyme. The first five form the preparatory phase that consumes ATP, and the final five form the pay-off phase that generates more ATP than was spent.
Each glucose molecule yields two pyruvate molecules, two NADH molecules, and a net gain of two ATP molecules. The two ATP gained represent the difference between four ATP produced and two ATP consumed in the early steps.
Understanding glycolysis took nearly 100 years of combined effort. Louis Pasteur linked fermentation to living organisms in the 1850s. Eduard Buchner showed that enzymes alone could drive glucose breakdown in the 1890s. Arthur Harden and William Young identified key intermediates and cofactors between 1905 and 1911. Otto Meyerhof connected the steps in the 1920s, and by the 1940s the full pathway, now called the Embden-Meyerhof-Parnas pathway, was complete.
Glycolysis itself does not use oxygen. It operates entirely in the cytosol, converting glucose to pyruvate without any oxygen-dependent steps. Oxygen is needed only in downstream processes such as the citric acid cycle and electron transport chain. Under low oxygen, organisms use fermentation to regenerate the NAD+ that glycolysis needs to continue.
The Warburg effect, first described by Otto Warburg in 1930, is the observation that malignant tumor cells perform glycolysis at a rate about ten times faster than normal cells, even when oxygen is available. This elevated glycolytic activity is exploited clinically: a radioactive glucose analog called FDG accumulates in tumors and is detected by PET scanning to locate and monitor cancers.
Glycolysis is considered an ancient metabolic pathway. The reactions that make up glycolysis can take place in oxygen-free conditions resembling the Archean oceans, and can proceed without enzymes, driven only by metal ions. This makes glycolysis a plausible prebiotic pathway that may have originated before complex life existed.