Nicole Walker is a fictional character on the NBC soap opera Days of Our Lives, a long-running series about working-class life in the fictional town of Salem. She was introduced in 1998 by head writer Sally Sussman Morina, and executive producer Ken Corday. Actress Arianne Zucker has portrayed the character since her introduction to the series in 1998. In 2006, Zucker left the soap in pursuit of other acting possibilities. She returned to the role in 2008. In 2016, Zucker also appeared as Helena Tasso, a deceased woman who bears a resemblance to Nicole, in flashbacks. In March 2017, Zucker announced she would once again leave the role. She made her final appearance in the role on October 20, 2017. Following her departure, media outlets began to report that Zucker was to reprise the role for a short-term visit in December 2017 after being spotted on-set; Zucker explained her visit, stating that her daughter was included in the annual telling of the Christmas Story at the University Hospital. In June 2018, it was announced that Zucker would reprise the role of Nicole later the same year. She appeared for a few weeks in October 2018. Zucker later returned in April 2019, but as Kristen DiMera, who was posing as Nicole. Zucker then returned to the role of Nicole in September 2019.

Many of Nicole's storylines have focused on treachery, death, and love, with the character being portrayed as always in pursuit of finding true love and having the family she never had as a child growing up. The character is the daughter of Fay Walker and Paul Mendez. During her childhood, Nicole was a victim of child sexual abuse at the hands of her father, Paul, who forced her to do pornography in her adolescence under the name "Misty Circle". The character came to Salem as a small-town waitress, but almost immediately started getting involved with the major families that the show revolved around. While once being seen as a scheming gold-digger, Nicole has grown into a woman committed to finding love and being a good mother. She is known for her longstanding feud with her enemy, Sami Brady, her relationships with Eric Brady, Victor Kiriakis, Brady Black and EJ DiMera, and the 2009 Baby Switch story line which featured Nicole having a miscarriage; lying to her husband; and stealing Sami's baby, Sydney.

Zucker's performance in the role has been met with favorable reception from audiences and critics, having garnered her two nominations for the Daytime Emmy Award for Outstanding Supporting Actress in a Drama Series in 2010 and 2013. In 2014 and 2020, she received her third and fourth Daytime Emmy nominations in the Outstanding Lead Actress in a Drama Series category.