Donna has been lifelong friends with Eric, having grown up next door to each other in the fictional Wisconsin suburb of Point Place. As she puts it when he is leaving for Africa, "You've lived 20 steps away from me my entire life, and now what am I supposed to do without you?"Their relationship has been tumultuous at times, having suffered two break ups since the show began. However during the majority of the time since the show aired, Eric and Donna have been in a serious, stable relationship, and they often act as the "parents" of the group, being mature and responsible when their friends are not so. This was sometimes threatened by the fact that he feels inferior to her, especially during the third season when she gets a job as a radio personality named "Hot Donna."
Donna, the character, is an intelligent, witty, red-haired (she later changed to blonde after her marriage to Eric was called off), tall (5'10"), strapping, rather strong, athletic teenager with feminist ideals, who is outwardly confident and strong, sometimes to the point of coming across as arrogant or self-righteous, though usually laid back and easy going. She calls upon these personal qualities to deal with her personal issues, such as the shaky relationship of her father and mother, Midge and Bob Pinciotti, who had her when they were still in high school. However, she has some difficulty expressing her feminine side, for she views traditional feminine traits as restraining and outdated. She dislikes skirts, makeup, and dresses, and insists on wearing jeans at all times, but she took a stab at "being pretty" for her prom and for a trip to a night club, where the bouncer judged her "foxy".
Jackie appoints herself as Donna's best friend early on, often giving her advice that sounds superficial and useless but often turns out to be unnervingly true (example: Eric would never want Donna to be his girlfriend if she kept beating him at everything, especially sports). The haughty Jackie genuinely thinks that she's better looking than Donna and that Donna is in general not attractive, interesting or popular--yet still thinks Donna could do better than Eric. Though they're as different as night and day, Donna eventually accepts Jackie and decides to keep an eye on her and keep her out of trouble, since Jackie doesn't always show the best common sense.
Donna was very reluctant to have sex, but after a few false starts, she finally lost her virginity to Eric in season 2. At first she found it awkward and weird, but Eric persuaded her to give it another try and with "practice" she found subsequent sex more pleasant and even enjoyable. And to both of their delight, very frequent.
Towards the end of season 3 Donna's job as a radio DJ was taking priority over her relationship with Eric, causing her to blow their dates off. While Donna genuinely felt that she was right to do this and was simply following her goals through to their logical conclusion with wanting to be a journalist and a news woman, her actions provoked a bad response in the normally even-keeled Eric, who felt that Donna was not taking him and/or their relationship seriously. Eric finally broke up with her after she returned his promise ring and throughout season 4 much awkwardness ensued over rights to the basement and trying to find new relationships. Donna was a bit annoyed at just how many girls were interested in Eric and happily mocked him when his attempts at finding a new girlfriend backfired. When some of them worked, she didn't take it quite as well.
Her mother Midge leaving her father and moving to California, followed by her father's relationship with Joanne Stupac, did not help matters. Donna's life seem to be worsening for the sake of sit-com material.
In season 4 she started dating Casey Kelso (Luke Wilson), older brother of Kelso. Though a little flaky and rather older than her, Donna thought Casey was a real winner of a boyfriend, for he seemed to be sensitive, good natured, laid back, and easy going. She thought she'd hit the jackpot with Casey and everyone else agreed - except Eric, who saw Casey for what he was: an oversexed frat boy who just wanted to nail Donna and move on to the next girl. Eric tried to warn Donna but she ignored him, and he then threatened Casey that he would hurt him if he hurt Donna.
When Kitty saw Donna drunk in the middle of a school day at the Hub with Casey, warning bells went off in her head and she rallied together with Red and Bob to bring the relationship to an end with Eric overseeing the proceedings while Hyde, Kelso, Jackie and Fez listened from the kitchen. Donna was more than ready and willing to fight for Casey, whom she thought truly loved her, but Casey was not ready or willing to fight for her and he readily agreed to break up with her when Red put the pressure on. Casey lazily said that Donna was a great girl and fun to hang out with but he stated that a relationship with a younger girl had gotten to be too much of a hassle and dumped her right in front of her friends and family. The realizations of her own over-confidence, poor judgement and being dumped in front of the people who meant the most to her came as quite a shock to Donna, who regarded herself as an ideal feminist, but who'd fallen for the exact kind of jerk she always swore she'd never look twice at.
Hurt, humiliated and heartbroken, Donna turned to the one person she thought still truly cared for her - old boyfriend Eric Forman. Eric offered his sympathy, but when a shook up, crying Donna told him she wanted to be his girlfriend again, he refused, believing that she did not really want him for who he was but simply wanted a way to feel better about herself and would most likely dump him when someone better came along. A tearful Donna pleaded with him to take her back but he refused to be her "second choice". Was he just a rebound? Eric was unwavering in his decision, until his father and mother pointed out to him that he was being an ass. As Red put it, "What makes you think you'll do any better? What have you got to be proud of? The only thing smart about you is your mouth."
Unable to handle being rejected by her first love, an emotionally-wrecked Donna fled Point Place for California, where she crashed with her mother and tried to sort out her feelings. She decided she truly did love Eric and tried to call him but couldn't get hold of him; she suspected he no longer wanted her and moved on to another girlfriend and became rather depressed. But then, to her delight, Eric showed up in California looking for her, and the two reunited and returned to Point Place. In Season 5, Eric ignored the objections of their friends and proposed to her at the Water Tower and Donna accepted.
Once Red and Kitty found out about the engagement, they were shocked. Kitty in particular, reacted badly, claiming that Donna was trying to snatch her "baby" away from her. Despite enduring a great deal of flak from his dad (far more than usual), Eric stayed loyal to Donna, and finally Red accepted his son had become a man and gave them his blessing.Donna and Eric prepared to leave Point Place together and go to college in Madison. However, just as they were packing their stuff in the VistaCruiser, Fez and Laurie announced their marriage. Red was so shocked he had a heart attack, and as a result Eric had to stay in Point Place and help support the family. Donna also gave up going to college in Madison so that she could stay with Eric. Eventually though, their wedding fell through at the end of season 6 when Eric, worried that marrying Donna would eventually leave him because this isn't the life she wanted, didn't to show up for their rehearsal.
After Eric's departure from the show before season 8, it was assumed that they still kept the relationship intact. However, Donna told her friends that Eric had broken up with her on the 07 December 2005 episode of season 8, when Fez and Jackie suspected that she was cheating on Eric with the new guy, Randy. Donna told them that Eric did this three weeks earlier. There were hints leading up to the breakup when Eric called Kitty but not Donna, even though she was awake at 4AM waiting for him to call her. Also, when Donna was at the Formans' for Red & Kitty's 25th anniversary, Eric called his parents and Kitty gave the phone to Donna, but Eric spoke to her only briefly before bailing out, claiming he had to "go teach".
Eric and her shared a kiss after he returned to Point Place for New Years Eve. Before this, she dated Randy after the break up with Eric, and then realized her relationship with Randy would interfere with her plans on seeing the world, and a possibility that she was still in love with Eric so she broke it off. It is unknown whether the two got back together. Donna was last seen running upstairs to the living room in an effort not to call Red a "Dumbass".
In the episode "Eric's Birthday," Kelso mentions that Donna is older than Eric. Donna replies that she's only a month older. Her birthday was said to be in July. But because of Eric's birthday in May, and her being a month older, her birthday would be in June. Another mixup in her birthday is that in another episode, her birthday is taken place in February, about the time of Valentine's Day (even though the episode takes place late into 1979), which would conclude Eric's birthday is in March, which he delusionally prompted saying in a season 5 episode.
In the episode "Ice Shack", Donna reveals her favorite pizza topping, according to her, her last name is Pinciotti, and if she (and accidentally Eric) could change anything about herself it'd be "My Wiley Coyote feet."
Donna's aggressive attitude towards Kelso worsens as the series progresses as she becomes even more superficial and self-righteous with herself.
A bit of a running gag in the series is her constantly getting mad at Eric for even the tiniest mistake he makes. Though, this quickly made Donna very unlikable, and not worthy of having Eric as a boyfriend.
"What would you have done differently?"
(In Fez accent) "My name is Fez, I love candy! Whore! Good-day, I said good day."
"What the Hell?"
"I'm gonna kick your ass!"
"We're completely naked!"
"Oh my God."
"Dammit, I'm gonna snap his little ass like a twig!"
"Sounds like a song (Sings) Jackie loves the foreign guy, Hola! Tacos!"
"(Eric) That's more action then I've got in weeks.
"(Donna) Keep It up, and you'll be having sex with yourself."
"Keep in mind Hyde, your being called a Stooge, by a stooge, while a third stooge *Points to Eric* sits near by.