Like many others of his day, and maybe even now, Gerhard Kremer ran into problems when he began to think too much about religion.
He was born in 1512, in a little town called Rupelmonde in Holland. In his youth, young Gerhard was a Catholic, but after a private Kremer-versus-Kremer with his conscience, he emerged a strong and perfect Protestant.
This at the time was a rather dangerous denouement; he lived in a strongly Catholic part of Europe when the concept of cuius regio, eius religio (to each kingdom its particular religion) was rigidly enforced.
In 1544 he was arrested and accused of heresy, but was lucky enough to be acquitted on a technicality.
In any event, it seemed wise at this point for Kremer to move to a more tolerant environment, and so he went to live in Duisburg in Germany. He was by trade a maker of scientific instruments, but he progressed to become a talented cartographer - a map-engraver.
His family must have dabbled in the world of business, because when Gerhard began to acquire a reputation, he became known by the Latin version of his surname - Mercator, meaning "merchant".
Mercator's claim to everlasting fame is that he straightened out the loxodromes. A loxodrome is a curve drawn on a chart so that it cuts all the meridians at the same angle.
It is very convenient for mariners if a straight line drawn from A to B on a chart is loxodromic, because then the constant angle between this line and the meridians provide, when suitably corrected, a compass bearing that will take one directly from the first point to the second.
This was not possible on earlier maps: even on a spherical globe, a line drawn to preserve a constant angle with the lines of longitude becomes a spiral, circling closer and closer to the pole as the meridians converge.
To achieve the desired effect, Mercator had to depict the meridians as parallel north-south lines on his map, so that a straight line would cut them all at the same angle.
However, the effect of this requirement was to distort east/west distances in the higher latitudes - and hence both direction and area at any given point.
Mercator overcame the problem by gradually increasing the distance between the horizontal lines of latitude as he moved northwards on his map.
In this way he was able partially to correct for the distortion, and directional integrity was preserved throughout the chart - albeit at the expense of areal distortion.
Gerhard Kremer, alias Mercator, died 405 years ago today, on December 2nd, 1594.