Kelly Marlene Taylor, portrayed by Jennie Garth, is the lead female character of Beverly Hills, 90210 for the majority of the show's duration. Initially presented as a "spoiled teen vixen", the role was gradually expanded by producers. Subsequently, Kelly became instrumental in launching the first spin-off, was written with a more compassionate demeanor, overcame several perils and personal challenges, and attracted many romantic suitors and triangles. Appearing for the entirety of the series' run, the character is noted for her development from youth to adulthood.

Kelly appears prominently in a majority of the shows that compose the Beverly Hills, 90210 franchise. In addition to her role in launching the spin-off, Melrose Place, Garth was the first performer from the original show to be cast in the third spin-off, 90210. Having appeared in the most series premieres, as well as the most episodes of any figure throughout the continuity, she is the de facto central character of the Beverly Hills, 90210 franchise.

Garth's portrayal has earned recognition from critics and co-stars. In a 1995 article on the actress, TV Guide's Mary Murphy stated that, "Her signature role—the sensitive, seductive, and tortured Kelly Taylor—tapped into the very essence of teenage angst and brought her a huge cult following." Actors Jason Priestley, Grant Show, and Sara Foster have expressed admiration for Garth's work. In a 2009 article, Nellie Andreeva of The Hollywood Reporter called the character of Kelly "organic to 90210's setting."

Throughout the course of the first series, Kelly became one of the show's most developed characters. When introduced in 1990, she was presented as, on the surface, a stereotypical spoiled type who placed high value on a posh appearance and material possessions. However, the character would become increasingly layered as the series progressed.

The reasons for Kelly's behavior first started to reveal themselves in episode 7, "Perfect Mom", when Kelly was forced to confront her mother's drug addiction and alcoholism. Several of her friends, particularly the Walsh family and Andrea Zuckerman, first came to appreciate Kelly's difficulties in life when they saw her handle this problem. During episode 13, "Slumber Party," Kelly revealed that she was taken advantage of by a senior during her freshmen year in high school, which had led to a promiscuous lifestyle and reputation which deeply hurt her self-esteem. The others then began to realize that Kelly had been through more difficulties than they were aware of, and later, she and Andrea would become close friends. When Andrea was pregnant and was contemplating an abortion in season 4, Kelly was one of the primary people she reached out to.

Toward the end of the second season, Kelly met a man named Jake Hanson (played by Grant Show), an emotionally guarded biker who was slightly older than her. While Jake ultimately resisted their romance, citing Kelly's age, he admitted to admiring her for her heart and kindness. This story line was used to launch the spin-off series Melrose Place. Eventually, Kelly was revealed to have a notable conscience during a summer fling with Dylan McKay, the boyfriend of her friend Brenda, often being the voice of reason during their affair. Kelly went through a period of minor depression during her senior year in high school in season 3. The stress caused from her love for Dylan, someone who she could not be with because of his relationship with Brenda, added to her struggles. Even when Kelly dated Dylan out in the open, following his relationship with Brenda, it caused her to temporarily lose Brenda as a friend.

Also during this time, Kelly's mother had a new baby, Erin, got married, and put Kelly's childhood home up for sale. Self-consciousness over her figure, along with the anxiety she began to feel, caused her to lash out emotionally, abuse diet pills, and briefly lose control over her life. The character's physical appearance is shown to play a part in her development. At various points of the series, she won the title of Spring Princess at a dance and was voted her school's most beautiful girl. Kelly is aware of her appeal, but not to the point of conceit; instead, she is sometimes shown to be troubled by it. At one point, she entered a phase in which she felt that no one took her seriously, which was heightened when Dylan gave his manuscript to Andrea for review instead of to her. During this time, she began to feel that people only liked her because she was physically attractive.

Creator Darren Star has commented on the character's progression. In his DVD commentary of the episode "Spring Dance", Star notes Kelly's first attempt to romance Brandon Walsh, in which she'd embraced her role as Spring Princess and used a largely forward and aggressive approach. He goes on to state that in the fourth season, when Kelly was prone to expressing her affections in a more gentle and compassionate manner, she made a greater impression on Brandon. While pursuing Jake on Melrose Place, a confused Kelly eventually asks, "Don't you think I'm pretty?" This contrasts with her attitude one year later, when she becomes more interested in having others appreciate her for what lies beneath the surface. This development is standardized one additional year later, via her aforementioned second pursuit of Brandon Walsh, which ends in success.