This collection of biographical works is dedicated to the memory of Ludwig Prandtl on the occasion of his 125th birthday. Ludwig Prandtl, the founder of modern fluid mechanics in Germany, taught at the University of Göttingen for nearly 50 years. Prandtl was born on February 4, 1875, in Freising, Bavaria. After starting his university career in Hanover, he accepted a position at the University of Göttingen, where he also founded the Aerodynamic Research Institute, which still exists today as a DLR site. Among his colleagues and students were many renowned scientists such as Ackeret, Betz, Blasius, Blenk, Busemann, Görtler, von Kármán, Ludwieg, Oswatitsch, Schlichting, and Tollmien. His ideas and publications have influenced modern aerodynamics and fluid mechanics in many fields. Perhaps his most significant contribution was the introduction.