Why are Arsenal fans called Gooners and players Gunners?

A bunch of workers from the Woolwich Arsenal factory had laid the foundations of this club. They used to manufacture guns and ammunition, hence the name GUNNERS. A cannon was embedded in all arsenal crests over the years reminding us of its origins:

As for arsenal fans being called Gooners:

1. There was a hooligan element that followed The Arsenal in the 70'sand hence the word 'Goons' combined with gunners made it Gooners.

2. Some people simply believe it is a pronunciation alteration like the the Newcastle fans calling their town as toon.

Source: Quora.com / Jemal Desai