Rudolph Christian Karl Diesel was a German thermal engineer and inventor of the high-efficiency internal-combustion engine that bears his name.

Much of Diesel's life and brilliant career was tragic—from his business failings, to his struggles to translate theory into practice, to his chronic physical and mental ailments. Yet his research and engine prototypes laid the foundation for one of the world's most efficient and widely used fossil fuel engine technologies.

Diesel was born to German Protestant parents. His father, Theodor, a bookbinder, emigrated from Germany to Paris in 1850, and five years later married Nuremberg-born Elise Strobel, a teacher of German and English. The couple had three children—Louise (b. 1856), Rudolph (b. 1858), and Emma (b. 1860)— and were strict disciplinarians. French was spoken in the Diesel home, and Rudolph's mother also taught him English. Rudolph had few friends, but took an interest in technology, reinforced...