Truly, there aren't many characters in The Rocky Horror Picture Show. I will detail all of them except for the Transylvanians, and some other minor characters. 
The first two are the major focus of the story. Brad Majors and Janet Weiss, recently engaged and on their way to see the man who was responsible for their meeting. They are stranded in the middle of the night, and forced to approach a castle a few miles from where the car broke down. Inside, they find a strange cast of characters. The story centers around them and their night at the Frankenstein Place. Both Brad and Janet are very wary, curious, and very frustrated. In more ways than one...
These two are part of the strange cast of characters I mentioned earlier. Brad and Janet meet the look on entry of the Frankenstein Place, and are soon introduced to the whimsical and musical ways of the manor. Very mysterious, sending individual. Magenta is loud, and seems rather upset at times. Both of them love to do the Time Warp. Oh, and they are siblings. 
Columbia isn't truly an important character, but she adds a lot to the story. Later, you meet Eddie, whom she fell in love with. That's why everyone calls her a groupie. She also loves Frank, and tap dances very well.
Ah, the show stealing Dr. Frank N. Furter. He truly is the human embodiment of a mad genius. He created Rocky horror, and brought to life. However, Dr. Frank N. Furter is very special. He's a transvestite. In fact, he's a sweet transvestite, from transsexual Transylvania. His character is interesting, and often angry at times.
This is Rocky. He was a creation created by Dr. Frank. His character isn't very well adapted to the world yet. He can't speak very well, but he can sing. Also he's very muscly, and very confused. 
This is Eddie, an ex-delivery boy. He and Frank have a very...intense and violent scene somewhere near the middle of the movie. Eddie is very loud and energetic. He also really enjoys playing the saxophone and riding his motorbike.
This is Dr. Everett Scott. There's not much to his character except that he is Eddie's uncle, German, and affiliated with the Nazi party, as well as the FBI. He will stop at nothing to take Dr. Frank and his whole operation down. And Dr. Scott knows a very big secret that Dr. Frank has been hiding...
Lastly, we have the criminologist. He is the storyteller, and that man has no neck. That's pretty much all there is to him.
So, there you go. All of the important characters of the Rocky Horror Picture Show. I absolutely adore this movie, and I would recommend it to anybody who can stomach the intensity.
