At age 18, I entered the Jesuit order, was ordained as a priest at age 25, and taught philosophy, theology, and mathematics at Pavia until my death.
My fame is due to my last publication Euclides ab omni naevo vindicatus (Euclid Freed of Every Flaw), now considered a very important work in non-Euclidean geometry.
However, my ideas remained hidden in obscurity until my book was rediscovered by Eugenio Beltrami in the mid-19th Century.
My stated intent was to establish the validity of Euclid by using a reductio ad absurdum proof to discredit any alternative to Euclid's parallel postulate.
I was able to discount elliptic geometry (no parallels), but hyperbolic geometry (2+ parallels) became a real problem...leading me to finally conclude in desperation that "the hypothesis of the acute angle is absolutely false; because it is repugnant to the nature of straight lines."
My eponymic quadrilateral has two equal sides perpendicular to the base, but I was unable to prove that the congruent summit angles were right angles.
Giovanni Girolamo Saccheri (1667 - 1733)