Tsugumi Ohba (大場 つぐみ, Ōba Tsugumi, born in Tokyo, Japan) is a writer best known for the manga Death Note. His/her real identity is a closely guarded secret. As stated by the profile placed at the beginning of each Death Note manga volume, Ohba collects teacups and develops manga plots while holding his knees on a chair, similar to a habit of L, one of the main characters of the series.
There is speculation that Tsugumi Ohba is a pen name of Hiroshi Gamō. Pointing out that in Bakuman the main character's uncle was a one-hit wonder manga artist who worked on a gag super-hero manga, very similar to Gamō and Tottemo! Luckyman in all aspects. Also that the storyboards drawn by Ohba greatly resemble Tottemo! Luckyman in style.
Source: information is from Animanga Wiki.