Shiho Yuki
It's L Lawliet... it says so in both his profile and a bonus page in Volume 13 How to Read
Yeah. Totally.
Hideki Ryuuga was just one of the fake names he used so Raito couldn't kill him because that name was the same as a pop idol's.
So, even if Raito wrote down that name and it was his real name, the face of the pop idol might appear in his head and kill him instead, making L think he is Kira even more...