Kalle Väisälä (1893-8-19 à 1968-9-16), a Finnish mathematician and pedagogue, was born in Kontiolahti, Finland. Having a function-theoretic background, his his PhD thesis 1916 was anyway Über die algebraisch auflösbaren Gleichungen fünften Grades (`On algebraically solvable equations of degree five'). Professor of mathematics in University of Tartu (Estonia), University of Turku (Finland) and Helsinki University of Technology.

Väisälä was known as an excellent teacher and author of textbooks of mathematics. For schools he made textbooks of algebra and geometry, which was printed altogether 800,000 copies. He abandoned the Euclidean systematics and extended the school algebra to the differential and integral calculus. For orientating himself in the problematics he teached on the side in a school. Väisälä made also textbooks for university-level, the most known are Lukuteorian ja korkeamman algebran alkeet (`Elements of number theory and higher algebra'), Vektorianalyysi and Laplace-muunnos (`Laplace transform').