Her style represents her determined, understated personality: Her custom dress is a black dress and combat boots with a severe black haircut. Before her arrival at X Middle School, Third was sent to a reform school in Nepal for an incident involving a stink bomb and a piñata. Ingrid, another former delinquent and a certified genius (she becomes the smartest kid in X Middle School) due to her photographic memory, arrives at X Middle School and partners with Fillmore after he helped her clear her name in "Ingrid Third, Public Enemy #1". Her father is a professor and she has an older sister named Ariella. Her mother is seen but never mentioned. It is revealed in "The Unseen Reflection" that she played Little League for 2 years.
The new girl at X Middle School- a stern and brilliant goth girl. She has a photographic memory, which is a very valuable gift that helps her in investigations. She respects her partner and friend Fillmore for his redeemed (if not sometimes apathetic) ways. A rookie at Safety Patrol but far from insufficient.
Ingrid is the quiet type and speaks only when necessary, she maintains a rather goth aura (judging by her clothes). Although quiet, Ingrid is caring and determined, and is Filmore's best friend, and alongside Fillmore she shows her grand intelligence to assist in finding the culprit. She has a kind heart for those she doesn't believe are guilty and at times tries to look the other way. She has also shown a mean side when she and Fillmore fall out over opinions.
Ingrid has short black hair with curled fringe, green eyes, and rather pale skin. She usually wears a black dress with black boots and carries a black backpack.
- Photographic Memory: Ingrid's most useful skill is her photographic memory, it has helped solve multiple cases over the series and is also the cause of her extraordinary intelligence.
- Forensics: Ingrid was trained in some areas of forensics by Tahama, she also attained compulsory training when she joined the safety patrol.
In the past, Ingrid had been to a large number of schools. She is a very intelligent person and due to this it made her a target for teasing and bullying, this inadvertently turned her into a delinquent. After arriving at X Middle School, Ingrid was treated like a guest of honor by the principal however she did not wish to stay at the school so she took the blame for a crime that she didn't commit. She was prepared to be kicked out of school however Cornelius Fillmore stepped in and convinced her not to take the blame and together they proved her innocence and she ended up joining the Safety Patrol as Fillmore's Partner.
She has a father who is a college professor, and a big sister named Ariella. Professor Third is seen in two episodes ("Red Robins Don't Fly" and "A Cold Day at X"), Ariella is seen in the latter only.
- Ingrid makes a cameo appearance in "The Halloween Bash", an episode of American Dragon: Jake Long.
- It has been shown in one of the cancelled third season episodes that Ingrid and Fillmore's relationship would have become romantic.