This is one of the best all around sites that I have found. It is titled “The MacTutor History of Mathematics Archive.”
This is an award-winning site that links to all sorts of mathematics information.
Euler circuits were named after Leonhard Euler (pronounced “Oiler”. You might wish to check out this interesting and important person in the history of mathematics.
Hamiltonian cycles are named after William Rowan Hamilton:
Klein bottles (Problem 60) are named after Felix Klein: