Rock Lee (a.k.a. Thick Eyebrows, as Naruto likes to call him) is a genin level ninja at the beginning of the series. Just like his row model Gai-sensei, he is a taijutsu specialist. Lee is incapable of using ninjutsu or even genjutsu. But due to Lee's great determination and extreme hard work, he was able to counter this great weakness by specializing in taijutsu.
In Lee's schooldays everyone thought he would never be able to become a ninja, simply because he can't use ninjutsu and genjutsu. But Lee has great determination, and said to himself that he could be a very strong ninja that only uses taijutsu. That's when he met Gai-sensei. Gai is also a ninja that only uses taijutsu. Gai-sensei became Lee's teacher and row model, and he taught Lee everything he knows now.
Lee also has a crush on Sakura. At first Sakura didn't want anything to do with him because he looks weird. But after saving her life and the fight with Gaara, she is starting to see what's so special about him: his unstoppable determination. Lee's training consists of physical training only. He always wears extremely heavy weights around his ankles. Lee only takes them off in 'life and death' situations. When he does this, his speed and strength increase dramatically. But Lee's true power lies in the fact that he can open several chakra Gates. After opening several of his Gates he can temporarily even triple his chakra, which makes him inhumanly fast. The downside of this technique is that it does severe damage to his body, that's why Lee can only do it for a very short time. If he can't finish his opponent before his body receives too much damage, he's done for.
Another one of Lee's talents is the Drunken Fist mode. When he drinks even one drop of alcohol, he will become an unpredictable and unstoppable force and it will cause him to destroy everything or everyone near him, be it a friend or a foe.
Lee became a chuunin during the timeskip to Shippuuden. He has also improved his taijutsu greatly, and is now able to recover from using the Chakra Gates quickly with minimal to no damage to his body whatsoever. Lee still has a fiery passion towards tough missions and training.