Georg Mohr
Jørgen Mohr was a Danish mathematician, known for being the first to prove the Mohr–Mascheroni theorem, which states that any geometric construction which can be done with compass and straightedge can also be done with compasses alone.
1 April 1640
Born on the same birth day (1 April): Dan Flavin • David N'Gog • Dennis Kruppke • Emperor Go-Saga • Mitchell Robinson • O. W. Fischer • Paul Manafort • Sonia Bisset • Vitorino Antunes • William Manchester
Born in the same month (April 1640): Gaspar Sanz