The protagonist in the best-selling fiction book of all time.
Spolier Alert: Jesus dies.
Also used as an exclamation of shock. It can be used with the conjuction of another word inserted between 'Jesus' and 'Christ'.
1) Reference to Bible
Pastor: So have you accept Jesus Christ as your Lord and Saviour?
Jessica: Oh wait, you mean that dude with the beard who's the main character in that popular bullshit book where magic happens? That one? Nah... did you hear I'm officially atheist?
2) - Shock
Ally: Did you hear Dan got into jail?
Ben: Jesus Christ! How the hell'd that happen!?
3) In conjuction with another word.
Tom: So what answer did you get for 5c on the maths homework?
Olly: Jesus rollerblading Christ, I forgot we had homework!
Lolita: So... when's your birthday again?
Beth: Jesus fucking Christ Lolita, how many times do I have to tell you?