Leonhard Euler ( ; Swiss Standard German , German Standard German ) (15 April 170718 September 1783) was a Swiss  mathematician, physicist, astronomer, logician and engineer who made important and influential discoveries in many branches of mathematics like infinitesimal calculus and graph theory while also making pioneering contributions to several branches such as topology and analytic number theory. He also introduced much of the modern mathematical terminology and notation, particularly for mathematical analysis, such as the notion of a mathematical function. He is also known for his work in mechanics, fluid dynamics, optics, astronomy, and music theory.

Leonhard Euler Telescope, or the Swiss EULER Telescope, is a national, fully automatic  reflecting telescope, built and operated by the Geneva Observatory. It is located at an altitude of at ESO's La Silla Observatory site in the Chilean Norte Chico region, about 460 kilometers north of the capital, Santiago de Chile. The telescope saw its first light on 12 April 1998 and is named after the Swiss mathematician Leonhard Paul Euler (1707–1783).