http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Napier.html

By 1571 Napier had returned to Scotland for he was present at his father's
second marriage which took place in that year. It was in 1571 that Napier
himself began to make arrangements for his own marriage but it was at nearly
two years before that took place. In 1572 most of the estates of the Napier
family were made over to John Napier and a castle was planned for the estate
at Gartness. When the castle was completed in 1574, Napier and his wife took
up residence there. Napier devoted himself to running his estates. This task
he took very seriously and, being a great genius as an inventor, he applied
his skills to these tasks. He approached agriculture in a scientific way and
he experimented with:-


> … improving and manuring of all sorts of field land with common salts,
> whereby the same may bring forth in more abundance, both of grass and corn
> of all sorts, and far cheaper than by the common way of dunging used
> heretofore in Scotland.

The above is quoted in [11] without reference to its origin.
Napier took part in the religious controversies of the time. He was a fervent
Protestant and published, what he considered his most important work, the
Plaine Discovery of the Whole Revelation of St. John (1593).
Napier had been a fanatical Protestant from his days as an undergraduate at
St Andrews. He wrote the Plaine Discovery of the Whole Revelation of St. John
according to his preface:-
> … for preventing the apparent danger of Papistry arising within this
> Island…
In fact there were good reasons why Napier thought that a change in the
religious situation in Scotland might occur, for there had, for some time,
been rumours that Philip of Spain might invade Scotland. The Plaine Discovery
of the Whole Revelation of St. John did gain Napier quite a reputation, not
only within Scotland, but also on the Continent after the work was translated
into Dutch, French and German. Gibson, in [11], remarks however:-
> … I suppose that there are few indeed of the present generation who have
> read, or even heard of, the book; whatever its merits may have been they do
> not appeal to the modern mind…
Napier's study of mathematics was only a hobby and in his mathematical works
he writes that he often found it hard to find the time for the necessary
calculations between working on theology. He is best known, however, for his
invention of logarithms but his other mathematical contributions include a
mnemonic for formulas used in solving spherical triangles, two formulas known
as Napier's analogies used in solving spherical triangles and an invention
called Napier's bones used for mechanically multiplying dividing and taking
square roots and cube roots. Napier also found exponential expressions for
trigonometric functions, and introduced the decimal notation for fractions.



> [Napier] used frequently to walk out in his nightgown and cap. This, with
> some things which to the vulgar appear rather odd, fixed on him the
> character of a warlock. It was formerly believed and currently reported
> that he was in compact with the devil; and that the time he spent in study
> was spent in learning the black art and holding conversation with Old Nick.
>


Pictures of JN at
http://www-gap.dcs.st-and.ac.uk/~history/PictDisplay/Napier.html