Tough call. I'm not sure I'd call Euclid a "founding' text. More like an early compilation, I would think, but I'm willing to be wrong.
Newton was kind of funny about publishing. If it weren't for Halley, he STILL might not be published. Also, folks of that era might be a bit confusing to today's reader as the tended to mix (and often confuse) mathematics, philosophy, religion, astronomy, physics, and maybe alchemy and astrology.
You could find a decent text on Math History. It may mention various texts of some importance. One that comes to mind is by Bertrand Russell, but you couldn't read it - trust me on this. Generally, you will find that mathematics spreads out very broadly very early - after the calculus (1800+). It is said by some that Jules Henri Poincare (1900ish) was the last to comprehend the whole of mathematics. I'm sure that is a gross overstatement of Mr. Poincare's knowledge, but it illustrates the point that no ONE person could do it any more.
There is a link to your right, "Famous Mathematicians". You can read for hours!