A somewhat socially inept but optimistic boy, Eugene is the class Jinx despite his name meaning "born lucky". Despite the misfortune for which he is known, probably his second-most-notable trait is his cheerful and plucky attitude. He enjoys musical theater and is prone to impromptu public dancing and singing.
He has orange hair, which is mostly short, except for a section in the front, which sticks up. His head is oddly-shaped, with the bottom half shaped like a bean, and the top cylindrical, with his long nose in the middle of the two. He has a long mouth going across his face, and freckles under his eyes. He is somewhat short and wears a white t-shirt, blue shorts, and socks with sandals. His underwear is often showing, in a constant state of a wedgie.
He is prone to several forms of misfortune and is often bullied by his fellow students, although most such occasions are usually at the hands of genuine bullies such as Wolfgang or Helga. Since Arnold has inadvertently caused Eugene's misfortunes several times (killing his fish, destroying his bike, ruining his birthday, etc...) this had once caused Eugene to conclude that Arnold is a jinx, as every major misfortune Eugene had involved him. However, in the episode "Mugged", Arnold rescued Eugene from street thugs who were trying to steal his mallomars and macaroons.
But many misfortunes in Eugene's life took place (not seen on the show) when Arnold was not present; nor were the many minor accidents (crashing his bike, falling down, etc.) that he experiences every time he appears. The possible reason for his bad luck is that he was born on Friday the 13th (revealed in "Friday the 13th"). Accident-prone Eugene is the subject of most of the scrapes, bruises, and general misfortune in the series.
According to Craig Bartlett, Eugene is "kind of 'proto-gay', so he's uncomfortable getting together with any girl." Examples of this are seen in "School Play" and "Married", though he had no problem kissing Lila for the play in "Eugene, Eugene!". His orientation is subtly hinted at in the series: his room is decorated with rainbows and unicorns ("Eugene Goes Bad"), and he complemented Curly's dress in "Ghost Bride".
- Eugene is allergic to cats ("Eugene's Pet").
- Eugene had a pet rabbit once which gave him nightmares ("Eugene's Pet").
- Eugene is known throughout the school for his bad luck.
- Eugene has a peculiar fondness for strained beets. ("Coach Wittenberg")
- Eugene reveals himself to be an Eagle Scout, even though in real life you have to be at least 11 years old to be one ("False Alarm").
- Eugene appears to enjoy synchronized swimming, as shown in "Synchronized Swimming".
- Some of the accidents and misfortunes inflicted on Eugene occurred while he was riding his bike.
- Craig Bartlett confirmed in an interview that Eugene is Jewish, although his ethnicity and religion are never revealed on the show.
- "Horowitz" is a Jewish surname.
- Strangely, he is nowhere to be seen in "Harold's Bar Mitzvah".
- His catchphrase is "I'm okay", although, in earlier episodes, it was "I'm fine".
- Earlier in the series, Eugene's hair was a dark orange-brown color, but throughout the series, it fluctuated to and from a slightly lighter shade until finally retaining the lighter shade in Season 4 and onward.
- In "Hey Arnold!: The Jungle Movie", it is revealed that Eugene is allergic to pitaya.
- In the episode "False Alarm" in Arnold's rendition of what happened Eugene responds to the name Melvin.