4. Pierre-Emerick Aubameyang: Borussia Dortmund to Arsenal, £55m

Arsenal have signed Gabon striker Pierre-Emerick Aubameyang from Borussia Dortmund for a record price of £56m. Arsenal officials said the 28-year-old, the 2015 African Footballer of the Year, had joined on "a long-term contract". Aubameyang will wear the number 14 jersey at Arsenal.
The Gabon international comes as a key signing for Arsene Wenger, especially after the sale of Olivier Giroud to Chelsea and Alexis Sanchez to Manchester United.
Aubameyang scored 141 goals in 213 games for Dortmund, including 21 in 24 matches this season. Even though Aubameyang has not played in the Europa League this season, he cannot play for Arsenal in it because his former club, Dortmund is now in the same European competition.