At first glance Ataru might seem like the average 17 year old high school boy, but Ataru is just about the most notoriously unfaithful, unlucky and lecherous idiot to have ever been born.

Ataru Moroboshi is possibly the unluckiest boy in the universe. Ever since he was born he's been a bane of the entire town of Tomobiki's existence. Born on a day that was simultaneously Friday the 13th, The date of a major earthquake and Butsumetsu (a very unlucky day in the Buddhist calendar). He has a knack for drawing bad luck to himself. He began to attract evil spirits, weirdos and then came the aliens. Starting with Lum, the alien girl that would change his life forever.

Ataru vehemently denies that he is married to Lum. He constantly runs away from her and rejects her affections. Partly because he feels that the restrictions of matrimony would put mean an end to his "girl-hunts." But also because Lum always zaps him with electricity everytime he does something stupid. Despite his protestations and poor treatment of Lum, Ataru really loves her. But his problem with commitment keeps their relationship from progressing. Once it a while he'll give indications that he loves Lum but then goes on to say that he also loves Shinobu, Sakura, Ran, Ryuunosuke, Ryouko, Oyuki, Asuka, Benten, Kurama (the list of women goes on and on). He is a polygamous man who's dream is to be master of his own harem. He takes Lum for granted, yet at times when he is faced with the possibility of losing Lum, Ataru's true feelings show itself. He realizes that she is the only one he truly loves. But can't admit it to anyone, not even to himself.

Above all, Ataru is an lecherous, tenacious skirt-chaser. He's a hopeless flirt, constantly lusting after other women. He relentlessly persues any attractive woman that crosses his path. He would do absolutely anything, no matter how absurd or physically impossible for a pretty face. Just about all women find his behavior utterly repulsive so his advances are consistently rejected. But none of this discourages Ataru. The more he's turned down the more motivated he becomes.

Ataru usually has an idiotic expression on his face. Yet he often spouts dramatic movie clichees and tries to look cool like a movie star. The problem is that Ataru isn't used to using his face muscles in a serious manner so it causes him great strain. Most of the time he uses this act to impress girls but it's pretty transparent to them that his intentions aren't so pure.

Ataru is just about the most tenacious boy you could meet. His libido gives him an incredible level of endurance that makes him seem almost inhuman at times. No matter how much he's smacked, punched, burned, blown up, shocked, pummeled or crushed he just keeps coming back for more. That's because Ataru can be such an idiot, that he never knows when to quit. He even seems to subconsciously enjoy getting abused by women. Ataru also has a lot of speed, especially when running away from something. He starts off as a rather cowardly figure, but soon after life with Lum, Ataru becomes quite fearless. He will attempt the most suicidal behavior without any regard of the consequences. Ataru appears to be an idiot, but he's actually very clever and can easily outwit anyone when it suits his purposes. But he's also a terrible liar so his attempts to deceive aren't always successful.