'Mini Mourinho', protests, young signings - five things about Leipzig
Leipzig's shock quarter-final win over Atletico Madrid sees the German club facing Paris Saint Germain in the Champions League semi-finals next Tuesday barely a decade since their creation.
Under Julian Nagelsmann, 33, a rising star among German coaches, Leipzig are also challenging Bayern Munich's domination of the Bundesliga.
Here are five things to know about the German club:
Leipzig were founded in 2009 when Red Bull took over the licence of fifth-tier side SSV Markranstaedt, near Leipzig, renaming and re-branding the club.
The city of Leipzig was chosen under advice from Germany legend Franz Beckenbauer, a friend of Red Bull owner Dietrich Mateschitz.
The team shot up Germany's league pyramid with four promotions in seven seasons.
As recently as 2013-14, they were still in the third division.
They reached the Bundesliga in 2016-17, making a flying start by briefly keeping Bayern Munich from first place in the league table before finishing second.
However, their Bundesliga arrival was met with hostility by Germany's established clubs, unhappy about their commercialism.
As the German Football League (DFL) insist a sponsor can not appear in a club's title, the fabricated German word RasenBallsport - literally 'LawnBallsport' - make up the initials RB.
Under the league's '50+1' rule, clubs must hold a majority of their own voting rights, but all Leipzig members are Red Bull employees.
"There's football being played to perform for a soda can," grumbled Borussia Dortmund chief executive Hans-Joachim Watzke in 2016.
Leipzig had the last laugh by beating Dortmund 1-0 in only their second Bundesliga match.
"11 cans beat an 11 who bottled it," retorted Leipzig's then-boss Ralf Rangnick.
However, some German fans were as unimpressed as Watzke.
A severed bulls head appeared pitch side when Leipzig opened their 2016-17 season with a narrow German Cup win over neighbours Dynamo Dresden.
Protests by home fans followed when Leipzig played away, particularly at Cologne, Moenchengladbach and Dortmund.
Flags bearing insulting or threatening slogans aimed at Red Bull boss Mateschitz often appeared when the club visited.
Things got out of hand in February 2017 when a large group of Dortmund supporters attacked visiting RB fans, including women and children, resulting in ten injuries.
Dortmund's then-captain Marcel Schmelzer scolded their fans, "we don't know you like that", in a video message and a stand was closed for the next home game.
Leipzig have always resisted the urge to use Red Bull's huge finances to buy established stars.
Cristiano Ronaldo and Lionel Messi were both considered "too old, too expensive" by Rangnick back in 2016.
The policy remains of developing young talent.
After becoming one of the Bundesliga's best central midfielders, Naby Keita was 23 when Liverpool signed him in 2018 for around 60 million euros ($70 million).
Timo Werner, 24, joined Chelsea in June after scoring 34 goals for Leipzig last season.
Captain Yussuf Poulsen, a veteran at 26, was signed in 2013-14 when Leipzig were in the third division.
In Nagelsmann, signed last season from Hoffenheim, Leipzig secured arguably Germany's brightest coaching talent, nicknamed 'Mini Mourinho'.
In the current squad, ex-Barcelona academy product Dani Olmo, 22, and US midfielder Tyler Adams, are both fulfilling promise after scoring on Thursday against Atletico.
RB Leipzig have made no secret of their desire to challenge the established order in German football by rivalling Bayern or Dortmund and finished third in 2019/20 to qualify for next season's Champions League.
In each of their four seasons in Germany's top flight, Leipzig qualified for Europe by finishing in the top six.
Under current Southampton manager Ralph Hassenhuettl, Leipzig finished their debut Bundesliga season in 2016-17 second to Bayern, leaving Dortmund third.
They are gaining valuable experience in Europe.
Leipzig were eliminated after the Champions League group stages in 2017-18 - their debut campaign - and also bowed out early in the Europa League last season.
However, this year under Nagelsmann, they finished top of a group containing Benfica, Lyon and Zenit Saint Petersburg, beat Tottenham in the last 16 and eliminated 2014 and 2016 finalists Atletico in the quarter-finals.