No one knows who first prepared hydrogen gas.
Henry Cavendish gets the credit for first isolating and studying hydrogen in 1766.
He produced the gas, which he called inflammable air, by reacting hydrochloric acid with metals such as zinc.
Zn + 2HCl → H₂ + ZnCl₂
Other scientists such as Robert Boyle and others also knew of the reaction between metals and acids.
Cavendish gets credit for the discovery because he was the first to study the properties of the gas systematically.
In 1783, Antoine Lavoisier recognized the substance as an element. He named it "hydrogène".
The first part of the name comes from the Greek hydro- stem of hydros "water". The second part comes from the French -gène, which comes from the Greek word gennao "I produce".
Hydrogen produces water when burned in air.
2H₂ + O₂ → 2H₂O
Hope this helps.