His nickname is derived from his hairstyle ("kakugari (カクガリ)" means "crew cut"), he has a large build. He is the least used of the stormtroopers and he often seen with Chibi. He is also the one who beats up Chibi the most.

When an alien race known as the Oni invade Earth, the chronically unlucky and unapologetically lecherous Ataru Moroboshi is selected as humanity’s representative in a duel for the fate of the planet! His opponent is Lum, the Oni’s very pretty princess, and it’s only thanks to Ataru’s unscrupulous behavior that he’s able to scrape out a win in a treacherous game of tag against her. Ataru thinks he’s had his lucky break at last, but when Lum takes a shine to him off the battlefield, the conflict follows him home as Lum invades not only planet Earth, but also the womanizing Ataru’s love life! 
 
(Source: HIDIVE) 

Note: Sentai has labeled the 1st and 2nd cour of this season as "Seasons 1 & 2". They have labeled the 3rd and 4th cours of the 2nd season as “Seasons 3 & 4”

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It all begins when aliens invade and threaten to conquer the Earth! However, one member of the human race is chosen at random to duel the aliens and save the planet: Ataru Moroboshi, a lecherous slacker from Tomobiki High School who begrudgingly participates. All he has to do? Play a game of tag and catch Lum — the beautiful alien princess in a tiger-stripe bikini — by the horns. Unfortunately for Ataru, it’s not so simple, since Lum can fly and deliver electric shocks! Perseverance pays off, but once he catches her, Ataru experiences another shock: He’s now Lum’s betrothed “darling” and she isn’t going back to her home planet anytime soon!
 
(Source: Crunchyroll)

What would you do if a tiger skin bikini-clad alien followed you to school every day? Poor Ataru's life has never returned to normal since volatile extraterrestrial princess Lum fell for him. Now an excruciatingly wealthy and genteel rival, Mendo, adds to Ataru's torment. Not to mention an unending stream of extraordinary classroom visitors and educational materials including incompetent cherry blossom spirits, a legendary nightmare-eating tapir, and a fourth-dimensional camera that breeches alternate realities.
 
(Source: VIZ Media)

The adventures of Lum, Ataru, Ten, and all the gang from Tomobiki continue in an assortment of new &ndash; but no less weird &ndash; stories. 
Watch as Lum, Ataru, and Shinobu encounter a rabbit-clad youth, enter the Room of Destiny, and get a glimpse into their futures in "Inaba the Dreammaker," or see Ran's plans to use a sherbet cone-producing bird to open a sherbet shop one hot Tokyo summer go terribly awry in &ldquo;Raging Sherbet.&rdquo; Ataru has yet another bad experience with Lum's cooking in "I Howl at the Moon".
 
(Source: Anime News Network)

Broadcast between episodes 21 and 22, the Spring special was a 1-hr show with 2 parts. The first part, "Urusei Yatsura All-Star All-Out Attack!", was a series of outtakes from the preceding episodes and recaps of the first 21 episodes. The second part, "The School Excursion! Run, Kunoichi!", was an original episode, but not part of the ongoing series.

Hiroyuki