E3 2013

Collector's Edition gets Niko as a parent from GTA IV.
But here's a video of how to look like Niko Bellic in GTA Online.
You'll pretty much be Niko himself or his son that looks like him.

You'll see his setup from the beginning on how to look like Niko Bellic, then the introduction to GTA Online with the customization as Niko and lastly gameplay as Mr. Bellic in San Andreas.

While the video shows the setup on "Appearance".
Here's a tutorial on how to do the setup of Niko:

~Heritage~
Dad: Special Dad - Niko Bellic (Collector's Edition only)
Mom: Any
Gender: Male
Resemblance: Male Completely

~Lifestyle~
Any.
Your choice of stats or choose stats that Niko would be suited for.

~Appearance~
Age: 30
Hair: Buzzcut
Hair Color: Dark Brown
Beard: Trimmed Beard
Hat: None (Optional)
Glasses: None (Optional)

~Clothes~ (Any, unless you want clothes similar to the original)
T-Shirts: Charcoal
Shirts: Track Jackets - Black
Pants: Sports Pants - Navy Track Pants
Shoes: Boat - Coffee

Niko's jacket is actually brown, but the ones I found are locked until you level up. Any jacket will do until you unlock a brown jacket similar to his original jacket if you really want to look like his original self from GTA IV. Show less