Daniel Christian Ludolph Lehmus (July 3, 1780 in Soest – January 18, 1863 in Berlin) was a German mathematician, who today is best remembered for the Steiner–Lehmus theorem, that was named after him.
His father Christian Balthasar Lehmus was a science teacher and director of a gymnasium in Soest, as such he took it upon himself to school his son.
From December 18, 1813 to Easter 1815 Lehmus was employed as a lecturer (Privatdozent) by the university, but in 1814 he became a teacher for math and science at the Hauptbergwerks-Eleven-Institut (mining school) in Berlin as well.
He published an elegant trigonometric solution of Malfatti's problem in the French math journal Nouvelles Annales de Mathématiques, but due to a copy error the author's name was given as Lechmütz.
[2][3] In 1840 Lehmus wrote a letter to the French mathematician C. Sturm asking him for an elementary geometric proof of the theorem that is now named after him.