Ryoko was designed - her whole body, appearance, height, hair color, eye color, etc. - were all planned out ahead of time. Washu used her ovaries and masu, an anti-matter based life form, as the genetic "father" of Ryoko. This is why Washu considers herself to be Ryoko's mother. As Ryoko's main power source, Washu gave her the three gems. The purpose of Ryoko's birth was never stated directly, but there were a few reasons. First of all, Washu wanted someone capable of harnessing and controling the gems' power.
Ryoko is powerful enough to bring out the full potential of the gems, the incredible ancient power of Jurai, including the ability to generate 10 Lighthawk Wings, as well as the Lightning Eagle sword. And secondly, due to a failed marriage in the past, Washu was forced to give up her only child, a baby boy. Ryoko is Washu's daughter after all, without having an actual father. I guess Washu just wanted a daughter. Washu had two students, Kagato and Yakage, both of which became her assistants during Ryoko's development. Kagato helped choose her design, while Yakage was in charge of Ryoko's sword. Washu raised and taught Ryoko, despite the fact that Ryoko doesn't think so (on account of her not remembering - refer to Tenchi Muyo Episode: "Hello Baby"). She loves her daughter very much, even though she picks on her constantly. Ryoko really is a science nerd like her mom; she just does a really good job of not showing it. Washu also gave a cabbit (half rabbit, half cat) named Ryo-ohki to Ryoko when she was little as her pet/spaceship. Ryo-ohki was created in a similar fashion to how Ryoko was created.
Kagato knew the potential of Ryoko's power, and he wanted it for himself. When she was a teenager (we'll say about physically 14 or 15 years old, being actually over 3000 years old), he managed to kidnap Ryoko, and at the same time, imprison Washu. He erased Ryoko's memories and brainwashed her; reprogramed to only obey him. She became his own private weapon, losing all sense of human emotion. In addition, Kagato took Washu's ships: Ryo-Oki, and The Souja and claimed them as his own creations, as well as claiming to be the creator of Ryoko. Kagato wanted the supposed greatest power in the universe, Tsunami, and used Ryoko to get it, starting her life as a Space Pirate, and eventually leading to her attack on Jurai.
The prince of Jurai, Yosho, chased Ryoko off the planet until they landed on the planet known as Earth. (Why does everyone want to come here?) Yosho defeated Ryoko using his sword "Tenchi", otherwise known as the master key, to take control of Ryoko's gems. He locked her up in a cave nearby, but instead of returning home (he was supposed to marry Ayeka), he decides to stay on Earth and live a normal life
(smart move buddy - stay away from Ayeka....).
700 years pass, and Ryoko is still stuck in that darn cave (tough break, Ryoko). Yosho's grandson, a teenage boy named Tenchi, had been interested in the legend of the "demon", who is actually Ryoko, locked up in the cave. His curiousity gets the best of him, and he unintentionally sets her free. At first, she is pretty pissed off with being imprisoned for 700 years, (wouldn't you be?) and decides to take out her anger on Tenchi, who happens to be Yosho's successor and blood relative (although neither of them know his grandfather is actually Yosho himself). Tenchi is able to stop Ryoko though, using the master key he found in her cave. She decides to stay with him, at first to try get her gems back, but then she ends up falling madly in love with him (it figures).
Ryoko is pretty old, almost 5000 years old. Like she says to Washu in the OAV, she's been alone for almost 2000 years. That was when she was under Kagato's control, since she doesn't remember anything before then. She has the ability to take on any age she wants, and does so, becoming physically 17 years old. Her gems provide her with many other incredible abilities as well, including flight, teleportation, an energy sword (lightsaber), the ability to shoot/throw energy beams, walk through walls and fire, breathe underwater and in space, regenerate, phase with matter, duplicate herself, summon demons, force field, telekinesis, and telepathy (w/ Ryo-ohki and Washu). Oh, and not to mention, super strength.
Ryoko's personality is definately one that stands out. She's loud, outgoing, arrogant, has a fiery temper, and can be a bit of an exhibitionist, but hey, don't knock her down just yet. She's sensitive, loyal and trustworthy - especially on the battlefield, has a good sense of humor (that's for sure), can keep a cool head (some of the time), and can be a real sweetheart at times, with a lotta love to give (to Tenchi that is). Her and Ayeka fight constantly, but I know they care deep down (VERY deep down - ever seen Time and Space Adventures Part 2?) Ryoko even saved Ayeka's life by risking her own (a few times, actually). Most of Ryoko's emotions come from her assimilation with zero (in the Tenchi OAV).
Ryoko loves to drink, sleep, take baths, gamble, and watch TV - Just about anything that isn't work. Ryoko's birthday is August 8th - translated to Earth's calendar, she's 5'5", her measurements are 31-21-32, and her blood type is AB. Just about all the information I've just given you is based on the Tenchi Muyo OAV. In the TV series Tenchi Universe, and in the new series Tenchi in Tokyo, some information varies. Ryoko's looks and personality pretty much stay the same though (except in Tenchi in Tokyo because that is one strange crazy show). All the stuff about the gems does not apply to the other series. In Tenchi Universe, Ryoko is just a space pirate who happens to land on Earth while being persued by Mihoshi. Ryo-ohki is still her pet/spaceship, but she has no relations to anyone else. Plus, she gains a rival - a bounty hunter named Nagi.
In the Tenchi In Tokyo series, Ryoko is still a space pirate, well....kind of. Her pirating days were pretty much over until Tenchi moved to Tokyo and got together with Sakuya (the evil serpant-like girl), then Yugi started showing up wreaking havok on the Masaki house, sending all her little cronies to trick everyone...you get the picture. Ryoko then gets back into the pirating business after meeting Hotsuma, but this doesn't last long. In the beginning, they all meet because Ryoko hires Washu as a partner as they travel to Jurai and steal the Lightstone. Of course, Ayeka, along with Sasami, won't allow Ryoko to get away so they trail her. So do Mihoshi and Kiyone of the Galaxy Police. Naturally, they end up on Earth. Ryoko and Washu try to make a run for it, but Ayeka's guardians Azaka and Kamidake find them. Ryoko decides to pick a fight, but is no match for the logs. Meanwhile, Sasami runs into Tenchi. To everyone's surprise, Ryoko puts in a last ditch effort and pulls out her trump card, the Jurai Lightstone.
She sticks it in her head and transforms into this "demon thing", a description nicely made by Tenchi as he and Sasami suddenly arrive on the scene. Ryoko decides to attack him, but the Jewels on the necklace he's wearing turns into a huge sword. He uses it to defend himself, accidently blasting Ryoko. She gets hurt pretty badly, and Tenchi feels all guilty about it. When she wakes, she decides to stay on Earth, and of course, everyone else wants to stay as well. In this series, Ryo-ohki belongs to Sasami, not Ryoko. I guess the writers figured it'd be better off this way since Sasami plays with Ryo-ohki all the time anyway.
I really enjoy the manga version, which takes place after the Tenchi Muyo! OAV. The series introduces Yakage, and Minagi, Ryoko's daughter...genetically anyway. Apparantly, Yakage had stolen some of Ryoko's DNA in the early stages, and used it, combining it with his own, to create Minagi. So tecnically, Minagi is the daughter of Ryoko and Yakage. Minagi looks identical to Ryoko, except for the scars on her cheeks. In the Manga, Yakage is really old and dying, and he is eventually killed by Tenchi, in a battle similar to that of his with Kagato. Minagi mourns her father's death, but eventually gets over it and decides to follow in her mother's footsteps and become a space pirate.
Well, I was thinking, and something happened to cross my mind. Ryoko is, after all, a goddess, and her mother is Washu. Since Washu's sisters are Tsunami and Tokimi, technicaly, that makes them Ryoko's aunts, right? Since Tsunami and Sasami are one person, does that make Sasami Ryoko's aunt? I really have no idea. It's just something I was thinking about. Wierd, huh? That means Ryoko and Ayeka are related! (If my theory is correct...imagine that) I guess it really is a small universe after all. ^_^