Harem Anime is comprised of the following concepts:
Literally hundreds of anime of this style come out in Japan, but how did it start? What is the origin of Harem Anime?
It is generally thought that Rumiko Takahashi (the best selling female Manga author in history) is the one who started the Harem genre, or at the very least the one who popularized it. Which one of her works can be considered as the first depends on how you define Harem anime. If you define it as one person (any gender) being romantically sought after by the majority of the cast, then the answer is Urusei Yatsura. If you narrowly define it as being a boy chased by several girls, then the answer is Ranma ½.
I know this is already answered, but I was just going to keep putting up longer and longer comments.
Technically the genre defining Harem Anime/Manga is Tenchi Muyo, so I think it deserves a mention.
The big distinction in favor of Tenchi Muyo is the romance component. While many earlier works may feature a popular guy who is chased by many women, a harem anime will attempt to incorporate romance. A Harem anime will also feature a seemingly worthless guy, who's hidden virtues (sometimes so hidden they don't exist) somehow win a scad of female attention.
Tenchi is this dorky-ish guy who fits the hard-headed/unconfident/awkward bill. "Tenchi-Muyo" is a bit of an omni-pun with many meanings, the most popular translation is "No Need for Tenchi" or "Useless Tenchi".
As harem anime would have it he ends up becoming the desire of a house full of beautiful women:
As luck would have it, Tehchi is also heir to the throne of a galactic empire. The chosen one who has light-saber battles against the forces of evil. And a hard working student who basically keeps his mouth shut, has nosebleeds, and gets overly embarrassed all the time.
He also saves the lives of most of the girls at one point in time or another. Each female character has a different reason for her attachment to him (which may vary depending on the continuity).
The above items, while the setting changes, are staples of the modern harem anime.
The genre is a result of pushing the everyman envelope. First the everyman is the chosen one, with powers, and a kingdom. Now all the girls like him, but he's just too thick to notice. Finally he basically has a house full of improbable women, who all want him. The everyman's dream come true. The story possibilities are endless, and even if you draw a blank for story, you can always have some kind of drama.
Tenchi came out in 1992, so it is 4 years younger than Ranma, and much younger than Yatsura. While Ranma is chased by several girls that he is technically engaged to, Ranma is unlike most harem heroes. He is confident, brash, and contrives humor from his many engagements in non-emotional ways. You'll never see the typical "guy accidentally falls and lands on one of the girls"-scenes. You will never see Ranma embarrassed about anything. However, it is a good candidate for a predecessor to Harem anime.
You've got to admit that Tenchi put the word "Harem" into the genre list.
This article says it is a toss-up between Urusei Yatsura and that Orange road show.
The article is long, and not sure if allowed to copy/paste, so here's the link.
The origin of Harem Anime isn't actually anime, in fact it came from America. Basically all Harem Anime are following the same formula that archie comics way back in the 40s. Multiple girls who fight over the main character A main character who is unable or unwilling to choose between the girls
So ya there all just variations on the archie formula, so remember archie was the real first Harem Anime.
