That Tierlist is my own opinion and I don't claim it to be representative or official.
Mathematicians are divided into 5 Tiers, meaning that every mathematician from higher Tier is (whatever does it mean)"better" than every from the lower Tier. However among given Tier, they are in random order - this is not from 1th to 50th but rather 1-10, 11-20, 21-30, 31-40 and 41-50. Order is not even related with chronology or fields of interests. One mathematician who should be on that list is boycotted for participating in Manhattan Project. I also did not put any mathematicians from before XVIIIth century because it is even harder to judge their results.
List is made for popularization of Mathematics (and for my fun while doing it). Don’t take it too seriously. I tried to be objective as possible. Unfortunately only 2 women are here.
Feel free to criticise in comments (unless You want to write that Ramanujan should be there). You can also write how many of them You have known before reading.
GOD Tier:
• Leonard Euler
• Carl Friedrich Gauss
• David Hilbert
• Paul Erdos
• Michael Atiyah
• Vladimir Arnold
• Hermann Minkowski
• Alexander Grothendieck
• Andriej Kołmogorow
• Grigorij Perelman
Tier 2:
• Georg Cantor
• Israel Gelfand
• Terence Tao
• Laszlo Lovasz
• Georg Riemann
• Stefan Banach
• Henri Poincare
• William Thurston
• Emma Noether
• Pierre Simon de Laplace
Tier 3:
• Neil Steenrod
• Godfrey Hardy
• John Littlewood
• Marius Linnik
• Neil Robertson
• Hermann Weyl
• Felix Klein
• Henri Lebesgue
• Ellie Cartan
• Joseph Louis Lagrange
Tier 4:
• Gustav Mittag-Leffler
• Camille Jordan
• Stephen Smale
• Tullio Levi Civita
• Sophie Kowalewska
• Felix Hausdorff
• Sophus Lie
• Andrew Wiles
• Heinz Hopf
• John Milnor
Tier 5:
• George Dantzig
• Alan Turing
• George Green
• Karl Pearson
• Samuel Eilenberg
• Wilhelm Killing
• James Sylvester
• Leopold Kronecker
• Nikolai Łobaczewski & Janos Bolyai