John Napier (1550 – 1617) was a Scottish mathematician best known for his formulation of logarithms which provided aid to mathematical calculations. In 1614 he published he book titled A Description of the Wonderful Law of Logarithms, which explained the technique of devising the logarithm (and differs from today’s concept of having a base raised to a corresponding exponent) and provided copious tables of logarithms to make calculations easier. Additionally, Napier was the first to popularize the decimal point as a means to separate the fraction from the integer.
The logarithm is simply the inverse operation the the exponential, in other words a logarithm can be used to undo what an exponent does. Logarithms were particularly useful in long distance navigation and astronomy whose calculations involved trigonometric functions.
In addition to publishing his impressive tables of logarithmic calculations Napier also found other ways to make mathematical calculations easier. He invented what is called the Napier bones, a manually-operated calculating devise used to calculate products and quotients.