Tell me when did the Borussia Dortmund found?

Context: Ballspielverein Borussia 09 e. V. Dortmund, commonly known as Borussia Dortmund, BVB, or simply Dortmund, is a German professional sports club based in Dortmund, North Rhine-Westphalia. It is best known for its men's professional football team, which plays in the Bundesliga, the top tier of the German football league system. The club have won eight league championships, five DFB-Pokals, one UEFA Champions League, one Intercontinental Cup, and one UEFA Cup Winners' Cup.

Founded in 1909 by eighteen football players from Dortmund, the football team is part of a large membership-based sports club with more than 145,000 members, making Borussia Dortmund the second largest sports club by membership in Germany. The club has active departments in other sports, namely in women's handball. Since 1974, Dortmund have played their home games at Westfalenstadion; the stadium is the largest in Germany, and Dortmund has the highest average attendance of any association football club in the world.

Answer: Founded in 1909