Loenhard Eular was one of the greatest mathematicians of all time. He was a Swiss man who spent a considerable part of his life in Russia. This meant that he had a Swiss and Russian influence. One of the problems for which he is famous is known as the Seven Bridges of Konigsberg. I find the context of this question interesting because he was perhaps the first to show that measurement, as in geometry, was not an essential part of mathematics. This problem could be reduced to a question of connection.
Nowadays sociologists & other social scientists make a considerable use of the
graph theory, in particular how people are connected, much of it developed by mathematics, to study how this affects our behavior. In other words, he solved the problem just by looking into the connection from location to location, he reduced the whole problem to just a simple question of connection. After he did this all that there was left to do was answer this one simple question. This was just one of the many things he is noticed for but this is perhaps one of the greatest due to the fact the he converted a huge problem, into a simple problem of connection.