...becoming the club's first icon.

I would say the club's first icon or iconic player.
Legend and legendary player might also work.

https://www.ranker.com/list/best-arsenal-players-of-all-time...

No one will doubt that Thierry Henry and Dennis Bergkamp, two members of the legendary "Invincibles" squad of the 2003-04 season that went undefeated, are club icons. Many of the team's best players have played for Wenger, whether forwards and strikers or midfielders and defenders, or anyone else on the roster.

Who are the greatest players in Arsenal history? Before Wenger, two of the greatest players in Arsenal history are Tony Adams and Ian Wright. Both these Arsenal legends were featured as part of the legendary 1989 First Division winners, that was the subject of Nick Hornby's Fever Pitch. The best and most memorable Arsenal players were a part of their championship squads, which there are plenty of.