Russian nicknames for Nikolai/Nicholas

[seizansha.livejournal.com]

this is all for fiction. He's 36 and half Russian only because both parents are half Russian. i've been looking for a nn that sticks with the ethnicity. i found some unusual ones under 'Nikolai' at babynamespedia, like Nil, but i'm looking for the most common and the proper spelling.(i keep calling him Nicky in my head.)