Jan Levinson was Michael Scott's boss, as well as his on-and-off girlfriend in the US version of The Office
Jan was part of the corporte sector of paper company Dunder-Mifflin. She would frequently visit the Scranton branch, mostly because Michael's antics would be extremely disruptive and borderline felonious.
Jan is initially portrayed as one of the many straight-people in the series, but after the recurring cast were given more depth, more and more of them appeared to be not as normal as initially thought. Jan would eventually follow this route, causing her to develop self-destructive tendencies and eventually lose her job. Durin her unemployment, Jan seemingly gave up on life and didn't bother looking for work for almost a year. Since then, Jan has enjoyed some success as both a buyer for a local hospital and as the head of the White Pages.
Jan has always seen Michael as an extremely immature man-child. When he surprised her by securing a client just by telling jokes, she began to see a different side to him. The two kiss and spend the night together. Jan had recently gotten a divorce, making her somewhat fragile at this point. The two try to keep professional after this, but its clear Jan has growing feelings for Michael, despite knowing that he's not right for her.
Its revealed that Jan and Michael went to Jamaica over the Christmas break. Michael blurts out that they had sex. The two then start a steady relationship, but Michael isnt happy living with her as Jan has become increasingly aggressive and domineering. He tries to break up with her, but Jan gets breast implants and entices Michael back in. After losing her job, Jan starts living with Michael, who's becoming stressed out from supporting her along with the aforementioned problems. The two have a very messy breakup whilst hosting a dinner party.
Sometime later, Michael found out that Jan was pregnant through artificial insemination (she made him get a vasectomy while they were dating). He feels he should do the honourable thing and help her raise the child, but Jan has since come to her senses and wants to stay single now.
Hunter was Jan's assistant while she was at corporate. Michael felt uncomfortable around Hunter as he was younger and better looking. When Jan was fired, she hugged Hunter and wished him good luck with his band. It was later revealed that Hunter wrote a song about Jan that heavily implied that he lost his virginity to her. Jan really likes this song, adding to the implications. Hunter was also privy to Michael and Jan's sex-life, as she frequently let him listen in on intimate phone calls with Michael.
Clark was a new employee at Dunder-Mifflin. In order to get Jan to be a regular customer, Pam and Dwight had him agree to be Jan's toyboy. After a three-week vacation with Jan, Clark comes back to the office, apparently not enjoying his time with her.
Carol was Michael's real estate agent. When the two began dating, Jan tried to be professional about it, but Michael made this difficult by bringing up the love triangle every time they met. Carol left Michael after tiring of his bizarre mannerisms, at which point Michael rebounded with Jan.
After Michael and Jan split up, Michael took an interest in Holly, only for Jan to reappear heavily pregnant. After meeting Holly, Jan noticed a spark between her and Michael and told Micheal to not date her. Michael was torn between the two, but ultimately learned from his past mistakes and picked Holly.
It was revealed in one episode that Jan believed Pam and Michael were ex-lovers. Pam continually denied these rumours, to no avail. When Pam and Jim were invited to Michael's place for a dinner party, Michael suspected that Jan might have poisoned his meal. Pam found this idea ridiculous, after all, she was the one Jan considered a threat!