Heidi Klinger is a minor character in eighth grade at Kadic Academy . She first appears in the episode X.A.N.A.'s Kiss and appears to have feelings for Odd, and agrees to go out with him. It is revealed earlier in the episode that the main reason Odd asked her out was that he claimed she was the only girl in the 8th grade that he had not yet dated, except for Sissi and Aelita. She agrees to go out with him, before being kissed by a Polymorphic Clone of Jeremie. Currently, she is another one of many of Odd's ex-girlfriends.
It is revealed in the episode Aelita that Heidi Klinger told the entire school that Odd's feet smell. When Odd confronts her about it, asking if his feet smell a little, she retorts, "A little? Just make sure you and your sneakers don't come within fifty feet of me", envoking laughter from the rest of the group.
Heidi often acts as a extra or background character, and cameos in many episodes. For example, in the episode Wreck Room, Heidi asks the William Clone to open the refrigerator in the Rec Room. To prevent embarrasment due to the clone's dim-wittedness, Yumi offers to open it instead.