MAY CONTAIN SPOILERS Matilda Lynn Seiler is one of the main characters in the alternate universe fanfic Double Down and Return to Highland by NeonHomer. She is a full twin sister of Daria Morgendorffer, having been born minutes after Daria.
Born in Highland, TX, on November 8th, 1980 (the date used in the Double Down for Daria and Matilda's birth) to parents Helen Morgendorffer and Jake Morgendorffer. Just starting out in their lives, they discovered Helen was having twins. Unable to financially support two children, they gave up the 2nd born for adoption. Matilda's adoptive father, James Seiler, was being tutored by Helen after she graduated law school.
After some discussions, James, and his wife Sarah, decided to adopt the 2nd Morgendorffer child. They were there for the birth, with James cutting the cord for "their" child. The name they gave her was Matilda.
Shortly after her birth, Matilda moved to the town of Edgewood, which is approximately 50 miles from the town of Lawndale. Like Daria, she had her troubles in school and in life. When she was 13, she attempted suicide, as the result of "getting into something she shouldn't have". She was committed for 72 hours.
She has lived in Edgewood for most of her life, until she discovered her twin sister. A short time later, they moved to a house in Lawndale so Matilda could be closer to her sister.
Matilda is an identical twin sister to Daria. Therefore, she looks almost identical to Daria, except that she wears a different style of glasses (described as more oval shaped compared to the round shape Daria wears), has a lighter shade hair color and different hair style. She wears a similar outfit to Daria, except for the colors (dark blue jacket and a light blue shirt). As she herself has said "I wear what I wear for my own personal comfort. I don't dress to impress anyone."
Matilda is skilled in Aikido and other martial arts as a way to bring mental focus. She is on par with Daria for intelligence. She also has her driver's license, and a little mischievous. However, she is a little more "personable" than Daria.
Alternates to Alternate Universes
It is stated in the fic Return to Highland that Matilda is married to Tristan Mathiesen, taking on his surname. However, NeonHomer clearly states that this fic is an "Alternate Universe based on an Alternate Universe", and that it is not an indication of what will happen in her life. (This is based on the fact that Double Down is the "fic of record" for Matilda, and Return to Highland is an AU based on that fact.