Well, I've finally done it. It's long and rambly, because I'm a long, rambly person, but I hope it's useful. Be warned: this contains spoilers for the entire run of Farscape, right up to the end of the series. Which, by the way, you should watch. The Sci-Fi Channel is re-running the whole thing in October, in preparation for the new mini-series. Just FYI.
Anyway, here ya go.
Chiana:
Chiana's species is Nebari, and her original homeworld was Nebari Prime. Nebari culture is brutally opressive, with a high emphasis on conformity. The Nebari Establishment does not condone outlaws, criminals, rogues, or misfits, who it often subjects to a long and scary brain-washing process called "mind-cleansing."
Chiana, being a free spirit to say the least, did not do well in this environment, and applied, along with her brother, for permission to leave the planet. They were both rather surprised when it was granted, but later found out the reason they were permitted to leave: as part of a routine "medical examination," they had both been infected with a dormant virus, which, like many other expatriate Nebari, they were expected to help spread throughout the galaxy via sexual contact. The virus could be remotely activated by the Nebari at any time they chose, killing all infected hosts and leaving a great many planets weakened and vulnerable to Nebari conquest. (The Nebari, by the way, are pretty damned scary. You don't hear much about them... They seem to mostly lurk in the background, letting the two main political powers in the galaxy fight it out between themselves, but they appear to have a higher level of technology than anybody else, and there's a very strong implication that they're just waiting for the right moment to pounce.)
Chiana's brother, Nerri, discovered that they were infected with the virus, and via a "contact high up in the establishment" obtained a cure for himself and his sister, so that they were no longer infected. Knowing that possessing knowledge of the existence of both the virus and the cure would make him a prime target for the Establishment, he parted ways with his sister (against her wishes and for her own protection), and joined up with the Nebari Resistance, working against the Establishment.
Chiana was later captured by agents of the Establishment, who wanted to get from her whatever information she might have about her brother and then take her back home for mind-cleansing, a fate she feared more than death. But the craft she was being transported in ended up getting into a collision with Our Heroes' ship, Moya, the Nebari were forced to come aboard while their ship was undergoing repairs, a lot of plot happened, and at the end of the episode Chiana's Nebari captor was dead, and she had more or less become a member of Moya's crew. (It's left entirely unclear whether she was the one who killed her jailor or not, and she has consistently evaded the question.)
Chiana didn't integrate into the misfit crew of Moya very well at first, not being the kind of person who works well in groups, but she eventually developed a stong bond with the human, John Crichton, and established a relationship involving "lots of really fantastic sex" with the Luxan, D'Argo. That relationship, alas, fell apart rather spectacularly in early season 3 when Chiana, knowing D'Argo was planning to ask her to marry him and desperately fearing the concept of committment, sabotaged things by sleeping with his son, Jothee. Things between them were very strained for quite a while, but they slowly rebuilt their friendship, and, by the very end of season four, had finally worked their way back to being lovers.
For some time, Chiana believed her brother Nerri to be dead, when a "life disc" implanted in her body and connected to a similar device planted in his ceased functioning. She later received information that he was alive and leading a resistance group, but did not want her to join him because it was too dangerous. Between the third and fourth seasons, she went looking for him, anyway, but didn't get very far, as there was an extremely large bounty on her head (mainly due to her association with John Crichton, the Galaxy's Most Wanted Man), and travelling around looking for her brother had become far too dangerous.
Also, some time in the third season Chiana was briefly possessed by an alien being called an "Energy Rider," which apparently left an interesting and disturbing legacy behind. She gradually developed strange and confusing "visions" of future events. Over time, these visions evolved and changed, until she was no longer seeing the future, but instead seeing the present in slowed-down, hyper-acute detail. These visions were often useful, but left her with debilitating headaches and periods of blindness, which gradually became worse and worse. At the end of the series, after one particularly draining use of the ability, she had failed to regain her sight at all.
So, that's her backstory, in a nutshell. As for her personality... Chiana is young, headstrong, and very independent. She's spent a lot of time on the streets, and claims to know how to "kick, kiss, or cry" her way out of any situation. She's an accomplished thief, and is practiced as using her sexual wiles to get what she wants. She's also fun-loving and very uninhibited. Over the course of the series, she's matured a bit, and learned how to exist as part of a group, but in most ways she's still the same old Chiana, and her motto is always "I do what I want to do."
Physically, she's a petite, attractive humanoid with gray skin, black eyes, and white hair. One of her most notable features is her strange alien body language, which tends to be very fluid and sensuous.