Russia and Euler, with their Russian traditional clothes, Kosovorotka. I color their with 2 colors from Hetalia Vol. 4 Special Edition. Half fail, but in the end, was very good...Axis Powers Hetalia is a copyright of Hidekaz Himaruya/Gentosha Comics.
Leonhard Euler (1707-1783) (C) Himself [link]
Art (C) Me.