Karl Weierstrass (1815–1897).
In undergraduate mathematics, we are confronted at an early stage with “Epsilon-Delta” definitions. For example, given a function 
The epsilon-delta concept can be subtle, and is sufficiently difficult that it has been used as a filter to weed out students who may not be considered smart enough to continue in maths (I know this from personal experience). The formulation of the epsilon-delta definitions is usually attributed to the German mathematician Karl Weierstrass. They must have caused him many sleepless nights.
of a number to take values from 1 to 9.
occurs more than 
of the time while 
is found in less than 
of cases (see Figure above). Specifically, the probability distribution is
for s=1.1 (red), s=1.01 (blue) and s=1.001 (black).
is chosen randomly with probability 
of being either plus one or minus one. It follows from the Kolmogorov three-series theorem that the series is “almost surely” convergent.
is hopelessly inefficient. With one million throws of the needle we might expect to get an approximation accurate to about three digits. The idea is more of philosophical than of practical interest. Buffon never envisaged it as a means of computing 
ThatsMaths 