Lavi is a cheerful red-haired Exorcist of mixed race, who aims to become a Bookman and is working along the Black Order just to be close to the events that must be seen. To help him, he developed an incredible memory: he is able to memorize every single aspect of something he saw, but he commented (in chapter 101) that he could identify "the key" (the key which Tyki Mikk gave) faster if he were to use both his eyes when sieving out the real "key" from the fake. He is 18 years old, and normally uses his left eye while the right eye is covered by an eye-patch (no one knows what his right eye looks like, because he hasn't revealed it yet).
He enjoys giving nicknames to various characters, naming Bookman "Panda" due to the thick black circles around his eyes, a converted Akuma "Chomesuke", and Arystar "Kuro-chan" in the anime and "Kro-chan" or "Krorykins" in the manga. He is the only character other than General Tiedoll to call Kanda by his given name (that name being Yu, also translated as Yū or Yuu), and apparently speaks to him outside of missions, a fact that was shown when he called Allen "beansprout" (モヤシ, moyashi), saying that if Kanda could call him that, Lavi could as well, as he is the same age as Kanda. He has a habit of teasing Allen, and deems himself as his big brother. A recurring gag in the series is Lavi's fondness for beautiful older women, whenever he sees a woman his type (Example: Eliade, Lulubell, Chomesuke, Anita) he'll yell out "Strike!" with hearts in his eye.
It is later revealed that his name, Lavi, is just an alias (his 49th, to be exact). He previously used the name Deak (ディック, Dikku), as revealed by a past memory while in Road's dimension. He had cast aside his old name and background to show his commitment to being a Bookman. It was also revealed that Lavi was once cold and indifferent to others, for a Bookman only lives to view and record history and that humans are nothing more than 'ink' on a page. However, over time, Lavi's personality changed and he began to truly care about others. He slowly casts aside his identity as a Bookman in favor of his protecting his friends; as shown when he thought that Allen was killed by Tyki Mikk tried to avenge Allen by attempting to kill Tyki himself.
There are many different translations of his name, such as Ravi, Rabi, Labi. But found in the D.gray-man Omake from episode 61 the correct spelling is Lavi