The Wuppertal native has racked up 264 Bundesliga appearances since joining the club at the tender age of 12, setting an example the club's breakthrough flock of talent would do well to follow in the years ahead.
Yurchenko aiming high
One player in particular who could benefit greatly from 27-year-old Castro's experience is new midfield recruit Vladlen Yurchenko. The Ukrainian Under-21 international has scored four goals in as many pre-season outings so far this summer and now has his sights firmly set on establishing a place in the Leverkusen engine room.
"I always wanted to play in a top league in Europe," Yurchenko told bayer04.de. "The way Leverkusen set up against [my former club Shakhtar Donetsk in the UEFA Champions League] really impressed me. I'm going to give it everything to make sure I play as often as possible. I want to play my part in the club's success."
It goes without saying Leverkusen's Ukrainian whizz will be in esteemed company at the BayArena. The likes of Castro, Heung-Min Son and Stefan Kießling are already household names in Germany's top tier, while the summer signings of Josip Drmic and rising star Hakan Calhanoglu are a clear signal of intent from the Werkself hierarchy.
"I'll be wearing the number ten shirt," the former Hamburger SV relegation saviour explained. "The number means a lot to me, it makes me mentally stronger. I used to wear it when I played for the Karlsruher youth team. I had the number nine shirt at Hamburg, so it's great to be handed the number ten again."
Early season yardstick
Leverkusen's new Zehner was one of a handful of blossoming Bundesliga stars to emerge in 2013/14, 18-year-old Bayer 04 duo Julian Brandt and Levin Öztunali very much included. The two German youngsters are currently on UEFA European Under-19 Championship duty in Hungary and will almost certainly have a role to play under new Leverkusen head coach Roger Schmidt upon their return.
After all, the 47-year-old strategist made a name for himself blending young and old at Red Bull Salzburg; not to mention playing a style of football with striking similarities to that of Jürgen Klopp's Borussia Dortmund. Will he be able to emulate BVB's tipping-of-the-balance success on German soil? Tune in to the two sides' Matchday 1 meeting at Signal Iduna Park to find out.
Stefan Schinken/ Adaptation by Christopher Mayer-Lodge