Weierstrass was a very influential teacher, and his meticulously prepared lactures established an ideal an for many future mathematicians; “Weie-rstrassian rigor ” became synonymous with “extremely careful reasoning.” Weierstrass was “the mathematical conscience par excellence,” and he became known as “the father of modern analysis.” He died in 1897, just one hundred years after the first publication, in 1797 by Lagrange, of an attempt to rigorize the calculus.