Derek Dietl is the hidden secondary antagonist of Monsters vs. Aliens. He is Susan's ex-fiance who worked as a weatherman for the local news station in Modesto, California.
He is voiced by Paul Rudd.
At first he is seen in the news reporting the weather and giving a message to Susan. Then he and Susan start having a conversation. He tells Susan that they are going to Fresno instead of Paris. After Susan gets hit by the meteor, she goes back in and starts the wedding. Then Susan starts growing which surprises him and looks on in disbelief as the government takes her away.
Revealing His True Colors
After a long absence, Susan goes to the news studio where his show is filmed. Susan speaks to Derek about getting together again. However, Derek reveals his true colors and reveals to her that he only liked her to get high ratings and that she is "casting a big shadow" over him and just walks off.
 After the death of Gallaxhar, everyone praises her and the other monsters for saving the world from the invasion. Then Derek arrives and tries to get her back to get higher ratings and gain more fame. But Susan flicks him only to be caught by B.O.B who tells him off, now already knew his true self and humiliating him in process. He tells the camera person to stop filming. It is unknown what happened to him afterwards, but he presumably got fired from his job and went out of business.
Derek is very ambitious, intelligent, opportunistic, manipulative, deceiving, and selfish, so he jumps at every opportunity to enhance his career whenever one presents itself, making him place his job before anything else, including his relationship with Susan (for example, he cancels their romantic honeymoon in Paris in favor of his weatherman promotion in Fresno). All this time he was hooked on his goal to get popular by his show.
Derek is a slender man who dresses nicely and has a handsome hairstyle.
- Initially, Derek is presented as a neutral character, but after Susan's accident, he becomes something of an antagonist towards her.
- He is also similar to Chad Charming from Disney's Descendants, as they are both manipulative for high ratings.
- Given that Susan aka. Ginormica's primary inspiration was Nancy Archer, Derek may greatly inspired by Harry Archer as he and Susan had strained relationship even with Susan herself mutated into a giant.