Onizuka is a reformed biker gang leader who has his sights set on an honorable new ambition: to become the world's greatest teacher... for the purpose of meeting sexy high school girls. Okay, so he's mostly reformed. 
However, strict administrators and a class of ruthless delinquents stand between Onizuka and his goal and they will use any means, however illegal or low, to drive the new teacher away. Perfect, because Onizuka's methods won't be found in any teaching manual; he cares about the difference between legal and illegal activities about as much as he cares for the age difference between himself and a high school girl. 
So get ready for math that doesn't add up, language you'd be slapped for using, and biology that would make a grown man blush... unless of course, you're the Great Teacher Onizuka. 

 Note: Episode 1 has an airtime of 48 minutes.

Former juvenile delinquent Onizuka finds himself thrust into to role of high school teacher, facing students who behave just as he used to and an administration that doesn't trust him. Using the brash an unorthodox methods he picked up in his youth, Onizuka manages to reach through to his kids and help them with their problems. (Source: Tokyopop) 
Notes: 
- Won the 22nd Kodansha Manga Award for Best Shounen Manga. 
- The chapter count includes the 7 chapters extra GTO: Great Toroko Oppai♡ (Tomoko's Big Adventures) published in volumes 11 and 12, and one extra published in volume 25.

Seinen