While i would say that Sheldon looks like a textbook INTP and his behaviour indicates that really strong, if he has Asperger Syndrom or is somewhere else on the spectrum he could be INTJ. People with Asperger can somtimes look like TI-User and Si-user even if they aren't.
Finch from POI is an INTJ. Root is not, not at all. I can't decide if she is either ENTP or ENTJ. "Hiw badly did you have to break it to make it care about people so much" sounds a little bit like something an inf. fi would say. Not what an tertiary Fi would say. INTJs aren't as cold as they often appear.
Gandalf is an INFJ. He is quite the INFJ stereotype.
Sauron is an ENTJ. I am not saying that all INTJs are frail, but when a guy smashes a gigantzic hammer in faces of people to send them flying, tertiary se is more likely then inferir se. And he didn't have a plan form the beginning. And I am not saying that INTJs can't be charming, but in his eraly days Sauron was very charismatic and use this to his advantage. This seems more directly out of the ENTJ than the INTJ playbook. I am mean, come on. He is an tyrannical evil overlord in thick armor. That is an ENTJ cliche.
When it comes to INTJs in pop culutre, i think ENTJ and INTJ get mixed up a lot. No, not all Es are unreflective and impulsive. No, not every cool character is an INTJ. When it comes to comes to spotting the differences betwenn NTJs I would focus on Se and Fi, since the first two functions are used whith each other anywas.