#3 Cesc Fabregas
Cesc Fabregas was considered one of the best midfielders in the world when he left Arsenal. The Spaniard was Arsenal's captain at the time of his departure and was truly the heartbeat of Arsene Wenger's side.
Fabregas' creativity and passing ability in midfield was unmatched in the Premier League, and he also had a penchant for chipping in with goals as well. He left Arsenal for his boyhood club Barcelona in 2011 in search of silverware. This would turn out to be a good decision by the Spaniard, however it greatly weakened Arsenal at the time.
Arsene Wenger's side lost their leader and talisman in what was one of the toughest periods for the club.
#2 Robin van Persie
The player who took over from Fabregas as captain, Robin van Persie, had struggled with injuries throughout his career. But he was entering his prime when Arsene Wenger handed him the armband.
The Dutchman filled the role spectacularly, becoming the club's most important player and one of the best strikers in the world. Van Persie won both the Premier League Golden Boot and Player of the Year in the 2011-12 season. However, it would end up being his final season at Arsenal.
After a long-winded transfer saga, the striker did the unthinkable and joined Arsenal's storied rivals Manchester United in 2012. Arsenal not only lost their captain and talisman, but also, strengthened their rivals in the process. Van Persie went on to win the Premier League with United in his debut season, which was incidentally the club's record-breaking 20th title.
#1 Thierry Henry
This is where the club's downfall started. The departure of Thierry Henry truly saw Arsenal go from perrenial title challengers to fighting for a top four finish. The Frenchman was the best player in the Premier League during the time of his departure.
However, it was a heartbreak in the Champions League final the season before for Arsenal. With that and the uncertainty over Arsene Wenger's contract situation at the club, Henry decided to leave Arsenal and join Barcelona in 2007. Wenger, on the other hand, decided to stay at the club and take it in a newer, younger direction.
Henry's departure signaled the end of an era at Arsenal. Arsene Wenger decided to put his faith in the likes of Fabregas, Van Persie, Tomas Rosicky and Alexander Hleb. He banked on them to eventually lead the club back into the fight for silverware. This, however, was not to be, and the club ended up suffering a decade-long trophy drought.