Homer's personality is one of frequent stupidity, laziness and explosive anger. He also suffers from a short attention span which complements his intense but short-lived passion for hobbies, enterprises and various causes. Homer says of himself, "When I'm passionate about something, I see it through to the end." For example, he converts his garage into a bar to spite Moe, the bartender, spent a whole episode studying and emulating Thomas Edison, convinced all of Springfield that the Rapture was imminent, and attempted to expose a plot to trade Springfield's baseball team out of state
by going on a hunger strike.

Homer is prone to emotionalism. For example, he gets very envious of his neighbours, the Flanders, is easily enraged at his son, Bart, and is repeatedly physically abusive towards him.

While Homer has repeatedly upset people and caused all sorts of mayhem in Springfield, these events are usually caused by either his explosive temper or a lack of foresight. Except for expressing annoyance at Ned Flanders, Homer's actions are usually unintentional.

Homer has a sense of humor similar to that of Mel Brooks. Homer tends to derive amusement from the misfortune of others. He thinks the loneliness of his father and Marge's mother is funny, and laughs hysterically at things such as a man getting hit in the groin with a football.

Homer can also be extremely jealous and attention-seeking, often leading to fistfights, such as one with former President George H. W. Bush. After being the center of attention in a yard sale, Homer's thunder is stolen when Bush and his entourage move in across the street. Unhappy with the attention being diverted elsewhere, Homer escalates a hostile situation with Bush after the former president spanked Bart for shredding his memoirs.

Homer is a chronic petty thief and borderline kleptomaniac, stealing everything from TV trays to power tools and air conditioners from Ned Flanders. He has also stolen golf balls from the local driving range, coffee mugs, pens and computers from work, and beer mugs from Moe's Tavern. He is also known to go through his neighbors' trash, scavenging such odds and ends as coathangers, copper wire, old newspapers and estrogen medicine.

Despite his vices, he can be a surprisingly good father, husband and friend, selling his ride on the Duff blimp to enter Lisa in a beauty pageant, giving up his chance at wealth so Maggie could keep a beloved teddy bear, using a nuclear pile to threaten a crooked businessman who swindled Bart, giving up his dream job at the bowling alley to return to work at the Nuclear Power Plant in order to afford his third child, risking his own safety to prevent Bart from skateboarding over Springfield Gorge, and even saving Ned Flanders from ruin by advertising Ned's business. He remains faithful to Marge, despite having opportunities to cheat on her with other women.

Despite their differences, it can be argued that Bart is his favorite child. On many occasions , when Homer tells a joke in public, Bart is often the only one who laughs, and does so quite loud. Also, whenever Homer comes up with a crazy scheme (such as selling grease for money), he finds Bart is the one child who will stand by him. Homer, for his part, stands by Bart and when all others had labeled Bart as rebellious and bad, Homer was the one person who stood up for Bart. Many fans speculate that Homer shows so much favoritism towards Bart because Bart reminds him of a young version of himself. Like Bart, Homer was lazy, unfocused, and largely dissrespectful of authority as a child. The two share an enjoyment of simple humor and often find themselves bonding over jokes at someone else's expense, even members of their own family ( "You don't win friends with salad.")

Homer has been bald since the mid 1980s, largely due to the fact that every time Marge was with child Homer would have a nervous breakdown and tear out large portions of his hair. Another explanation of his hair loss points to an Army experiment. He briefly regained all of his hair in another episode using a hair regrowth formula called Demoxonil, which showed his natural hair colour to be chocolate brown.
Although he only has two hairs on top of his head, Homer maintains a combover. On several occasions, he has also lost these last two hairs, such as an episode when Mr. Burns pulled them out. In another episode, he grew two additional hairs while Bart was away at camp, due to reduced stress thanks to Bart's absence.

His beard, while usually shaved, remains a constant, rough '5 o'clock shadow'. On several occasions, his beard has been shown growing back within moments of being shaved. He has also let it grow out several times. It is revealed in the episode "Three Gays of the Condo" that he also will resort to using spray-on muzzle for the 5 o'clock shadow look.

Homer has had two hair styles. The first was made up of "U"'s (right-side up and upside down) around the back. Homer's hairstyle was changed by Matt Groening because "it was faster to draw". Homer's current hairstyle is made up of //// lines around the back. On a side view of Homer's head, two of these bumps (//) and the shape of his ear make up the letters MG, for Matt Groening.