Hans Christian Ørsted (Oersted) was born August 14, 1777 in Rudkøbing (Rudkjobing), Denmark (island of Langeland). Oersted received a doctor of philosophy degree in 1799 from the University of Copenhagen. Like many of the great scientists of late 18th and early 19th centuries, Oersted studied many fields including chemistry, aesthetics and physics. In addition to his scientific work he also was a published writer and poet.
The discovery that puts Oersted on my list of giants was the connection between electricity and magnetism. The details of how this discovery happened are uncertain with three accounts by Oersted as well as information from students who were present at the time. See the biographies and articles linked below for some of the variations in the story. What seems clear to me is that although he was not specifically experimenting with a compass near a wire carrying an electrical current, he immediately recognized the significance of the observed effect. Oersted had seen the compass needle move and through later experiments and analysis demonstrated clearly the deep connection between electricity and magnetism, what we refer to today as electromagnetism. For this important work he received the prestigious Copley Medal from the Royal Society of London in 1820. His work was recognized in 1930 by naming the SI unit of magnetizing force (magnetic field strength) the oersted.