My characters are reflections of myself. Currently that would make 'Boulevard of Broken Dreams' (aka 'I Walk Alone') the theme for Alain, possibly also Sognec. Does not make him a loner per se, but he can be introverted and over-focused at times.
I've always wanted to use that for an Uru video, due to my deep association with the Honor Guard and my decision within their RPG story to declare myself 'true neutral' (did not side with Yeesha or DRC - I sided with 'Uru,' literally meaning Community).
Older possibilities for a theme:
-> Metallica's 'Frayed Ends of Sanity'
-> 'November Rain' (I believe is Guns 'n Roses)