Fun Facts
The fact that 1. FC Union Berlin reached the 2001 DFB-Pokal final and that mascot "Ritter Keule" swings his morning star at every home game — that's fairly well known in German football. But there are plenty of lesser-known fun facts about "Die Eisernen."
The Christmas Carol Singing: It's a "Union classic" that has since been copied by numerous clubs. Semi-officially since 2003, officially since 2005, nearly 30,000 people gather at the Stadion An der Alten Försterei shortly before Christmas for the now-traditional Christmas carol singing — mulled wine included. Pastor Kastner, successor to Pastor Müller, tells the Christmas story, the choir of the Emmy-Noether-Gymnasium sets the key and tempo, and a small brass ensemble provides festive-cheerful sounds. Songbook and candle are provided free of charge — "a small donation towards the club's youth development is always welcome," the Union website notes.
Union Berlin's first European goalscorer is Sreto Ristic: The former Stuttgart player, who scored five goals in 47 Bundesliga appearances for VfB between 1996 and 2000, found the net on September 20, 2001 in the 1-1 draw at FC Haka in Finland. It paid off doubly for him, as he had a goal bonus in his contract. In the second leg, Bozidar Djurkovic, Ferdinand Chifon and Hristo Koilow scored Union's goals. They remain the club's last European goals to this day.
Berlin's largest "real football stadium": The Alte Försterei, completely rebuilt in 2008/09 and 2012/13, with a capacity of 22,012 spectators, is the largest purpose-built football stadium in the German capital (as of December 2019).
They called them Sebastian: FCU strikers Sebastian Andersson and Sebastian Polter were the most prolific scorers in the Bundesliga promotion season 2018/2019, with twelve and nine goals respectively.

Top goalkeeper: Rafal Gikiewicz — goalkeeper number one at 1. FC Union Berlin — was the best keeper of the 2018/19 2. Bundesliga season with a Kicker rating average of 2.68.
Record goalscorers: German-Algerian Karim Benyamina is the all-time top scorer at Union with 87 goals in 213 competitive appearances. He is followed by Torsten "Tusche" Mattuschka with 70 goals in 299 matches and Brazilian Daniel "Texas" Teixeira, who scored 67 goals in 78 appearances (as of December 2019).
Attendance record: Two attendances of more than 74,000 in the Berlin derbies against Hertha represented Union Berlin's record for a league match — until the Bundesliga trip to Bayern Munich on October 26, 2019 (75,000 spectators).
Record transfer: According to Transfermarkt.de, Union Berlin's most expensive departure of all time (as of December 2019) is Bobby Wood. Hamburger SV paid a club-record four million euros for the American striker in 2016. Serious money in Köpenick at the time.