Slavoljub Eduard Penkala (April 20, 1871 - February 5, 1922) was a naturalized-Croatian engineer of chemistry and an inventor of the first mechanical pencil (1906) (then called "automatic pencil") and the first solid-ink fountain pen (1907). Also constructor of the first Croatian two-seat aeroplane (1909). He constructed and invented many other products and devices, and has under his name a total of 80 patents. Among his inventions are the hot water bottle, detergent, rail-car brake and anode battery. He was associated with "Radium Vinovica", a patent-medicine-like product, presumably either misleadingly named or dangerous quackery. Penkala was born in Liptowsky st. Mikulaš (in what is now Slovakia), added "Slavoljub" to his name after immigrating, and died in Zagreb of pneumonia at the age of 51.