#3 Ousmane Dembele
Ousmane Dembele was making his name in the French Ligue 1 when Mislintat scouted and brought him to Dortmund. He was bought in from Rennes and stayed for a year before joining FC Barcelona.
He had a relatively good season, winning the DFB Pokal and being named in the Bundesliga Team of the Season. He played 50 times for Dortmund, scoring 10 goals, including a goal in the 2017 DFB Pokal final win over Eintracht Frankfurt.
FC Barcelona swooped in on him immediately and made him the third most expensive footballer ever by paying Dortmund €105 million initially, making it a great bit of business for Dortmund.
Dortmund could potentially earn up to €130 million in performance related bonus and other clauses making great profits on a player signed just a year ago.