How does Pierre de Fermat's contribution apply to our world today?

Here's a perspective that may not be available in things like Wikipedia. Fermat did lots of important work in the mathematical discipline called number theory, about primes and integers in general. Long considered one of the purest sorts of mathematics, number theory started being used in the middle of the last century in computer science and coding. One example: When people put their credit card numbers into web sites to buy things, it's safe because the information is encrypted, and what makes the encryption work is mostly lots of advanced number theory. So you could draw a logical connection from Fermat to the multibillion dollar ecommerce industry.