19th Century Pioneer

Gustav Robert Kirchoff (1824 – 1887).  Germany.

A German physicist that did important research in electricity and thermodynamics.
His early work on electrical currents and the flow of electricity in conductors established current and voltage laws that are know today as Kirchhoffs laws. 

Kirchhoffs 1st law states that the sum of the currents arriving at any point in a circuit must equal the sum of the currents leaving that point.

Kirchhoffs 2nd law states that the sum of the voltage drops in a circuit equals the total applied voltage.

These laws are important to remember when one performs circuit analysis.