what is his contribution in the field of mathematics?
He is the discoverer of logarithms, invented the so-called "Napier's bones" and made common the use of the decimal point in arithmetic and mathematics.
John Napier
John Napier is best known as the discoverer of logarithms. He also invented the so-called "Napier's bones" and made common the use of the decimal point in arithmetic and mathematics.

where does the irrational number e come from The first references to the constant were published in 1618 in the table of an appendix of a work on logarithms by John Napier. who is this person? He was a Scottish landowner known as a mathematician, physicist, and astronomer.
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John Napier [SEP] Introduction
John Napier of Merchiston (; 1 February 1550 – 4 April 1617), nicknamed Marvellous Merchiston, was a Scottish landowner known as a mathematician, physicist, and astronomer. He was the 8th Laird of Merchiston. His Latinized name was Ioannes Neper. John Napier is best known as the discoverer of logarithms. He also invented the so-called "Napier's bones" and made common the use of the decimal point in arithmetic and mathematics. Napier's birthplace, Merchiston Tower in Edinburgh, is now part of the facilities of Edinburgh Napier University. Napier died from the effects of gout at home at Merchiston Castle and his remains were buried in the kirkyard of St Giles.