Jan Kowalski (placeholder name)
In Polish culture, Jan Kowalski is a placeholder name for an average Polish person, the usage being similar to "John Smith" or "John Doe" in some English speaking cultures. The surname Kowalski/Kowalska is the second most common surname in Poland (140,471 people in 2009), with the leader being Nowak (207,348 in 2009).
Source: Wikipedia — Jan Kowalski (placeholder name) (CC BY-SA 4.0)