It is believed that writer Tsugumi Ohba is no one other than Hiroshi Gamou, known by manga series such as Tottemo Luckyman, which had a popular anime in the 90's.Another possibility is that it's Yuuko Asami, a Shonen Jump artist with titles such as Wild Half, Romancers and Jump Run. Given that Death Note was her first written manga, working with a pseudonym can be understandable.
And of course, there's also especulation on the possible idea that the L character is based on the physique and the personality of this mangaka, taking into account some elements such as:
-They use a pseudonym.
-Never been seen in public before.
-A snacks lover
-Thinking about things day and night.
-And the posture of sitting in a chair, hugging her (or his) knees.
In fact, he, (or she?) only communicates with the press through an avatar like this:
It's even hard to tell if it's a man or a woman.
Isn't this amusing? The fact that L could really exist in this world??? O_O
If she's actually a woman I can finally understand the whole yaoi KiraL going on XD