Chloe Anne Sullivan is Clark Kent's closest friend and superhero sidekick. She worked for years as a reporter for the Daily Planet, then managed the Isis Foundation. She recently joined Oliver Queen's hero team under the codename Watchtower.

Chloe's parents are Gabe and Moira Sullivan. Chloe has no siblings but has two cousins: Lucy and Lois Lane. Chloe is very close to her older cousin and the two look after each other.

After four years at Smallville High School, Chloe moved back to Metropolis after graduating in 2005. She has been attending Metropolis University as a journalism major, and was also an intern at the Daily Planet. [citation needed] She began writing obituaries and classifieds and answering the 24-hour news hotline, followed by small general-interest and current event articles. She, along with many other staff members, was fired from the Daily Planet by the paper's new owner, Lex Luthor.

After Chloe was fired from the Daily Planet, she became manager of the Isis Foundation, while also dealing with an infection from Brainiac's programming-- she acquired his computer intelligence and knowledge of the universe after he tried to re-wire her nervous system. After bouts of amnesia, eventually Brainiac was able to control Chloe completely until Clark and the Legion defeated him.

Due to her natural intelligence and computer skills, Oliver Queen chose Chloe as a part-time member of his team of superheroes, working as "Watchtower" in a mission coordinator capacity and other digital espionage.

Chloe cultivated a strong friendship with Lana Lang, despite their mutual affection for Clark. Initially a rival for Clark's affection, Lana came to see Chloe as her closest friend.

Since beginning an on-again, off-again relationship with Jimmy Olsen in 2006, Chloe has seemingly shed her crush on Clark and the two have maintained their close friendship after high school. She is part of a select group that knows Clark's secret. Clark is honest and open to Chloe, often asking her advice or support in his personal problems.

Chloe and Jimmy were unable to sustain their relationship through his difficult recovery and they divorced. She became a fugitive with Davis Bloome to try to keep him from killing Clark. Chloe and Jimmy reconciled and Chloe watched in horror as Davis and Jimmy killed each other while the Doomsday monster ravaged Metropolis.