Hydrogen was the first element created in significant amounts after the Big Bang.
During the first minutes of cosmic history, the universe cooled enough for protons and neutrons to combine in nuclear reactions. This period, called Big Bang nucleosynthesis, produced mostly hydrogen nuclei, along with substantial helium and tiny amounts of deuterium, helium-3, and lithium-7.
Hydrogen is the simplest element, with one proton in its nucleus. Most ordinary hydrogen in the universe is still in the form of single protons, while hydrogen atoms later became the raw material for stars and galaxies. The heavier elements found on Earth were made much later inside stars, stellar explosions, and neutron-star mergers.
A common misunderstanding is that all hydrogen formed instantly as neutral hydrogen atoms. The early universe was too hot for stable neutral atoms at first. Electrons joined nuclei much later, during recombination, about 380,000 years after the Big Bang. Hydrogen fusion in stars is a separate process from primordial nucleosynthesis.