Ted Mosby (Josh Radnor) was a relentless romantic who believed that he was destined to meet The One. Over nine seasons of How I Met Your Mother, he got into a handful of serious relationships and casually dated a few other woman in his quest to find his soulmate. Halfway through the series, Ted thought that he had met the perfect woman for him when he fell in love with a headstrong dermatologist.
Stella Zinman (Sarah Chalke) was introduced to the show in Season 3 when Ted visited a tattoo removal clinic. He had gotten a tattoo of butterfly on his lower back earlier in the season and hired Stella as his dermatologist to get rid of his drunken mistake. Ted immediately developed a crush on her but she made it clear that she was not allowed to date her patients. Ted persisted and kept asking her out up until the final session, but she explained that she was a single parent and rarely had time for dating.
Ted was determined to date Stella and managed to woo her with a cute two-minute date. They had been dating for about three months when she invited Ted to her sister's wedding, but he got cold feet and dumped her. When he realized he made a mistake, he decided to win her back by proposing to her. Despite being together for such a short time, Stella said yes. Considering she claimed that she was nervous about being in a serious relationship again, it was a major red flag that she would agree to marriage so quickly.
As their relationship developed, it became clear that Ted and Stella were not right for each other. She hated his favorite movie, he hated the idea of moving in with her in New Jersey, and she couldn't get over the disappointment of her previous relationship. Nevertheless, she decided that they should spontaneously get married when her sister's engagement fell through three days before the wedding.
Even though Robin (Cobie Smulders) had become part of the friend group and Stella didn't seem to have an issue hanging out with her, she was upset that Ted had invited Robin to their wedding. She felt that it was a bad idea to have an ex at a wedding because it could bring up unresolved feelings. Ted tried to convince her to reconsider and ended up inviting Tony, Stella's ex-boyfriend, to attend the wedding as well. It turned out that the only unresolved feelings at this wedding were between Stella and Tony. On the day of the wedding, Stella left Ted at the altar and ran away with Tony.
Seven months after their failed wedding, Ted bumped into Stella and Tony in New York. Tony offered Ted a job to make up for leaving with Stella but Ted declined it as he wanted nothing to do with Stella anymore. Tony dumped Stella after hearing Ted's feelings, and then she had the audacity to ask Ted to convince Tony to take her back.
Stella's character went from bad to worse in the following season when Ted discovered that Tony had written a movie about their love triangle. The Wedding Bride was a biased and dishonest recreation of Ted and Stella's relationship that made Ted seem like a villain. Stella's retelling of the relationship made Ted seem selfish and cruel, when he was the one who always compromised to please her. The film also contained intimate details about Ted and his personal life, indicating that Stella had shared this information with Tony.
Stella started off as a fun girlfriend who fit in with the group, but as the show progressed she became one of the most disliked characters in How I Met Your Mother's entire run. There were even a few incidents when Stella made decisions for their relationship without discussing things with Ted, but he gave in because he was so in love. Her legacy on the show is as the girl who rushed into almost getting married, ran off with an ex, and then violated Ted's privacy with an untruthful film about their breakup.
Even when Ted was hurt by Stella leaving, he realized that it was more important for her daughter to be reunited with both her parents and decided against confronting them. Ted certainly made some immature decisions when they were together, but Stella was out of line by making herself seem like the victim when she ended their relationship in such an ugly way. Although Ted dated some women who were very wrong for him, Stella was the worst love interest in the series because she had so little remorse for breaking his heart.