Mathematician, inventor and astronomer. Born at Merchiston Castle (Edinburgh) into a wealthy family, Napier was the eldest son of Sir Archibald Napier (1534 - 1608). He was educated at St. Salvator's College, St. Andrews and became a staunch Calvinist.
He devised "Napier's Rods" or "Napier's Bones" which permitted easy multiplication by addition. This led to his best remembered work: the concept of logarithms, which he described in Mirifici Logarithmorum Canonis Descriptio (1614). He also invented the decimal point and a hydraulic screw pump to remove water from coal mines. Napier also proposed a number of new weapons, including a device based on mirrors to set fire to enemy ships by focussing a high-intensity light beam, an armoured wagon and a submarine. He also experimented in agricultural improvement on his estates.
His son to his first wife, Elizabeth, became the first Lord Napier. In 1572, he married Agnes Chisholm and they settled on his family estate at Gartness, near Killearn (Stirling). Napier was buried at St. Cuthbert's Church in Edinburgh.