The Optimus G on Japan's Docomo network is an interesting device, as it ships with a mandatory access control system that basically prevents remounting system, reading boot, executing tasks with root privileges, and things of that nature. Thus, the root process for this version of the Optimus G was a tricky one.
A backdoor found by Android hacker giantpune will be used, which allows the bootloader to be unlocked, a modified boot.img to be flashed, and some security features to be disabled – ultimately allowing root access to be achieved.
Now that you have the basic idea down – a couple of noteworthy things:
Graphical glitches will occur while in the bootloader.