ANSWER
Avogadro was a lawyer, from a family of lawyers. In 1796 he earned a doctorate in ecclesiastical law and began his legal practice. He was only 20 years old at the time. Four years later he began studying mathematics and physics. By 1811 he published what became known as Avogadro's Law, which states equal volumes of gases at the same temperature and pressure contain the same number of molecules, regardless of the chemical nature and physical properties of the gases. This number of molecules became known as Avogadro's Number. Today that number is defined as the number of Carbon-12 atoms in 12 grams of Carbon-12, or roughly 6.0221367 x 10^23 (10 to the 23rd power, or the number represented by a 1 followed by 23 zeros.)
(Avogadro was also a Count, his full title being "Lorenzo Romano Amedeo Carlo Avogadro, Conte di Quaregna e di Cerreto". Get it? "Count"... "Number"... Ah, nevermind.)
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