Kathy Beale (also Mitchell and Sullivan) is a fictional character from the BBC soap opera EastEnders, played by Gillian Taylforth. Portrayed as "an attractive, bright, caring and highly moral woman", Kathy is one of the serial's original characters, appearing in the first episode of EastEnders on 19 February 1985. Taylforth was originally dismissed for the role of Kathy due to her young age, but was reconsidered when she impressed show bosses. Kathy remained in a prominent role throughout her original stint on the serial, featuring in high-profiled storylines involving her rape at the hands of James Willmott-Brown (William Boyde) and the discovery of a long-lost daughter, Donna Ludlow (Matilda Ziegler), after she was sexually assaulted as a teenager.

In 1993, after the character's marriage with her husband Pete Beale (Peter Dean) ended with the latter's departure from the square, Kathy developed a romance with Phil Mitchell (Steve McFadden) and they later had a son - Ben, who caused Kathy turmoil when he contracted a rare form of meningitis. The relationship between alcohol abuse and domestic violence was explored through Kathy and Phil in 1997, which led to their separation. Taylforth opted to leave the serial in 1997 and Kathy departed on 10 April 1998 after deciding to move to South Africa with Ben. Kathy returned for two separate guest stints in 1999, making her departure on 6 January 2000. Despite reports that Taylforth would be returning to the serial, Kathy was supposedly killed off-screen in a road collision in 2006 to facilitate Ben's reintroduction to the serial.

Taylforth reprised the role for a charity special in 2014. In the episode broadcast on 19 February 2015 to celebrate the show's 30th anniversary, Kathy made a surprise return to the serial - despite being presumed dead. It was confirmed that Kathy would be making a permanent return, and - after a guest appearance on 19 May 2015 - Kathy returned permanently on 17 August 2015. Taylforth was initially hesitant about her reintroduction storyline, which was inspired by the John Darwin disappearance case. Kathy's husband, Gavin Sullivan (Paul Nicholas), was also introduced following her return and their turbulent marriage was explored. Kathy later had an affair with Buster Briggs (Karl Howman), and became critical in the events surrounding Max Branning's (Jake Wood) revenge campaign Albert Square - in light of the "Who Killed Lucy Beale?" saga - when Willmott-Brown returned in his plan to recoup his relationship with Kathy by taking control of the square for her. Additionally, Kathy has had relationships and flings with Masood Ahmed (Nitin Ganatra), Harvey Monroe (Ross Boatman) and Tom "Rocky" Cotton (Brian Conley) and feuds with both Max and his wife Rainie Cross (Tanya Franks) over the custody of her adoptive grandson Steven Beale's (Aaron Sidwell) daughter, Abi Branning, with Sharon Watts (Letitia Dean) over her relationship with Ian, and Rocky’s niece Dotty Cotton (Milly Zero) who attempts to con her with Rocky.