Karl Scheele, the Swedish chemist, invented a method to commercially produce phosphorus. Prior to this phosphorus was produced by evaporating human urine. This invention of Scheele has made Sweden today the leading producer of matches. Well this is probably how much our books will tell us about Scheele. But Scheele, in spite of being poor and lacking proper apparatus had discovered eight elements "Chlorine, fluorine, magnesium, barium, molybdenum, tungsten, nitrogen and oxygen" and got credit for none of them. He also discovered ammonia, glycerine and tannic acid all breakthroughs that made other people wealthy.
Scheele discovered Oxygen in 1772, but for complicated, heartbreaking reasons could not publish his paper in time and the discovery was credited to Joseph Priestly in 1774. Chlorine was discovered by Scheele 36 years before Humphrey Davy and all textbooks credit Davy for it.
Scheele's downfall was probably his insistence on tasting a little of everything he worked with, including noxious stuff like, mercury, prussic acid (another of his discoveries) and hydrocyanic acid. Scheele's habit eventually caught up with him and in 1786, aged 43 he was found dead in his workbench surrounded by an array of toxic chemicals.
Coming to Humphrey Davy, he too was a prolific discoverer of elements. One after another Davy discovered 'potassium, sodium, magnesium, calcium, strontium and aluminium or aluminum (depending on which English stream you favour). His hoards of discoveries were because he developed an ingenious technique of applying electricity to molten substances- electrolysis. With this he had discovered a dozen elements. Davy had developed the addiction of inhaling nitrous oxide (laughing gas).
Davy knew about the anaesthetic effects of nitrous oxide. His wisdom tooth pain was killed by nitrous oxide, but he was so fascinated by its psychedelic effects that he did not bother to propagate it and for another 50 years, people had still undergo, surgeries without anaesthesia. Davy grew so attached to nitrous oxide that he used to inhale it three to four times a day and eventually in 1829 it killed him.