Since the Wolfenstein series often focuses on B.J. Blazkowicz as the protagonist fighting against the Nazis, he is very likely to be a main character in the 'Wolfenstein Graphic Novel'. Additionally, there might be other characters who play important roles. For example, there could be characters from the resistance movement who assist B.J. in his missions. There may also be key Nazi officers or scientists that are portrayed as antagonists in the graphic novel. Without having read it, it's hard to say for sure all of the main characters, but it will surely be centered around those involved in the battle between good and evil in the Wolfenstein world.
In the Wolfenstein novel, BJ Blazkowicz is highly memorable. He is like the typical hero, always ready to take on the bad guys and fight for what's right. Anya is also very memorable. She has a strong personality and her relationship with BJ makes the story more interesting. And there's Set Roth. He is a wise character who provides a lot of knowledge and guidance to the others.
The main character is BJ Blazkowicz. There are also other important characters like Anya Oliwa who is BJ's love interest and an important part of the resistance.