Georg Simon Ohm (1787-1854), a German physicist, in 1826 experimentally determined the most basic law relating voltage and current for a resistor. Ohm's work was initially denied by critics.
Born of humble beginnings in Erlangen, Bavaria, Ohm threw himself into electrical research. His efforts resulted in his famous law. He was awarded the Copley Medal in 1841 by the Royal Society of London. In 1849, he was given the Professor of Physics chair by the University of Munich. To honor him, the unit of resistance was named the ohm.

What he has discovered?

As a school teacher, Ohm started research on a new electrochemical cell which were invented before him by Alessandro Volta Italian scientist. Utilizing his own developed equipment, Mathematically given as $$\bbox[10px,border:1px solid grey]{ V = IR}$$

As a school teacher

Ohm became professor of mathematics at the Jesuits College at Cologne in 1817. The most important aspect of Ohm's law is summarized in his pamphlet Die galvanische Kette, mathematisch bearbeitet (1827; The Galvanic Circuit Investigated Mathematically). While his work greatly influenced the theory and applications of current electricity, it was so coldly received that Ohm resigned his post at Cologne. He accepted a position at the Polytechnic School of Nurnberg in 1833. Finally his work began to be recognized; in 1841 he was awarded the Copley Medal of the Royal Society of London and was made a foreign member a year later. The ohm, the physical unit measuring electrical resistance, also was named for him.