ISTJs are strict and serious, they like having things their way. They are also very clever, good at analyzing stuff and would most probably be the person who will help you with your homework, here are some ISTJ examples!  
Black Widow- The Marvel comics  
Vision- The Marvel Comics  
Electra- The Marvel Comics  
Winter Soldier- The Marvel Comics  
Spock- Star Treck  
Snape- Harry Potter  
Hermionie Granger- Harry Potter  
Sheldon- Big Bang Theory  
Big Macintosh- My Little Pony  
Elsa- Frozen  
Martha Jones- Doctor Who  
Castiel- Supernatural
 
And get other types down below!  
INTP pony  
INTJ pony  
ENTJ pony  
ENTP-green-viper.deviantart.com/art…  
INFJ-green-viper.deviantart.com/art…  
INFP- green-viper.deviantart.com/art…  
ENFJ- green-viper.deviantart.com/art…  
ENFP- green-viper.deviantart.com/art…