Mine's a pseudonym I used to put on my short films in high school and college (over 6 years ago), and it's got a long and boring story behind it... here goes:
Essentially, it comes from a background character mentioned in my favorite Lovecraft story "In the Walls of Eryx" along with a complete misunderstanding of the Japanese language.
My name is Matthew, en espanol Mateo, francais Matthieu, and so on and so forth. While pondering one day, "I wonder what my name would be in Japanese?" I found myself watching an old episode of Digimon, wherein one of the lead characters' english name is Mat, derived by abbreviating his Japanese name "Yamatomo". At this, I thought, "A-Ha!" and remembered the name "Matsugawa" from the Eryx story. Of course, I know now that my name is "Matto" in Japanese and it's not even really a translation, it's a phonetic re-interpretation because Japanese and Hebrew have no past relationship as languages whatsoever. And yes, I know I'm 6'4", occidental, brown-haired, and blue-eyed and therefore not remotely even mistakable for Japanese-looking, but my affinity for asian film caused me to use the name on my video works.
Appendix: My other frequently used username is recorder_manta, which is basically my self-indulgent dream of what my role and alias would be were I part of the Foxhound program. Recorder refers to my avid interest in most anything that has a 'record' button.