Thea Dearden Queen, also known as Speedy, is a fictional character portrayed by Willa Holland on The CW television series Arrow, created by Greg Berlanti, Marc Guggenheim, and Andrew Kreisberg. She is the maternal half-sister of series protagonist Oliver Queen / Green Arrow. Although an original creation to the series, she adopts elements from the DC Comics superhero Mia Dearden / Speedy, created by writer Kevin Smith and artist Phil Hester.

Holland was a main cast member on Arrow from its first season until its sixth, and also crossed over to the spin-off Arrowverse series The Flash. Although Thea Queen is loosely inspired by the existing comics character Mia Dearden, a sidekick of Green Arrow, the idea of Green Arrow working alongside his archer half-sister was later incorporated back into the comics in the form of Emiko Queen.

Thea Queen was born on January 21, 1995 in Star City to Robert and Moira Queen, (although it is later revealed that Thea is Malcolm Merlyn's biological daughter) and the younger half-sister of Oliver Queen. Though Malcolm was unaware that Thea was his daughter, and Thea was likewise in the dark, Robert was aware but still loved Thea like his own. When her father and brother were both presumed dead, Thea felt alone and disconnected from the world. She fell into a life of drugs and partying to fill the void left by her father and brother.

Thea is introduced as a senior in high school who is grateful to have her big brother back, but his disappointment in her lifestyle and the secrets he keeps from her about his five years away cause her to slip even further into drug use. On her 18th birthday, she is involved in a car crash while on the narcotic Vertigo and is subsequently arrested and sentenced to community service for 500 hours at CNRI (City Necessary Resources Initiative) under the supervision of Laurel Lance. Her addiction to Vertigo causes an animosity between her returned brother's alter-ego the Arrow and the drug's creator the Count.

Later that year, Thea falls in love with Roy Harper, a lifelong street criminal whom she meets when he steals her purse. Though he initially has no romantic interest in Thea despite an obvious physical attraction to her, mainly out of resentment because of her wealth, Roy later begins to genuinely fall in love with her.

After the Undertaking and Oliver's disappearance, Thea takes over his club, Verdant, while maintaining her relationship with Roy. That year, after learning of her true paternity from Slade Wilson, losing her club to Isabel Rochev (who had taken Queen Consolidated out from under Oliver), breaking up with Roy (now a member of Oliver's team and under the influence of Mirakuru), and the death of her mother, Thea decides to leave town. While waiting for her train, she is attacked by a Mirakuru-enhanced soldier and rescued by Malcolm, who reveals himself to still be alive. After discovering that Roy worked with the Arrow, Thea, betrayed once again, decides to go with her father and leaves Starling City and her family behind, with no intentions of coming back.

Thea begins the season in Corto Maltese receiving combat training from Malcolm, though she soon decides to return to Starling with Oliver. She also reopens her nightclub after Malcolm secretly buys the foundry from Queen Consolidated for her. She learns Oliver's secret identity as the Arrow when he shows her his hideout under the nightclub and begins to distrust Malcolm after learning that he already knows about Oliver's secret. She has a one-night stand with her club DJ, but he turns out to be a league of assassin spy. Thea is told that her father used her as a pawn against both Oliver and Ra's al Ghul by drugging and manipulating her into killing Sara Lance, she arranges for him to be captured by the League in retaliation. She reconciles with Roy but is nearly killed by Ra's and is brought back to life in the Lazarus Pit in exchange for Oliver joining the League of Assassins. Thea blames herself for letting her brother join the League. Roy breaks up with her when he leaves Starling City after faking his death, hoping that Thea can make a life of her own without him. He also leaves her his red costume which she wears to become a vigilante herself as his successor.

Thea works with Oliver and his friends in the fight against the terrorist organization H.I.V.E. By Oliver's request, the team refers to her in the field as "Speedy" (over her insistence to be called "Red Arrow"). Despite the enjoyment of being a vigilante, Thea's behaviour has become increasingly volatile and reckless when in the field, which Oliver realizes is a side effect of being in the Lazarus Pit. In addition, Thea helps Laurel to bring Sara back from the death in hopes of making amends towards the Lance family. Because of this, Thea is telepathically linked with Sara after her resurrection upon the Lazarus Pit. It is also revealed that Thea's Lazarus Pit side effect is able to counterattack Damien Darhk's life force drain in addition relieving her bloodlust temporarily. Thea is dying as the result of the Pit's restorative effect waning. With Tatsu Yamashiro's help, Nyssa al Ghul gives Oliver the 'Lotus', an elixir used by the Crescent Order that permanently reverses the effects of the Lazarus Pit, saving her life. She helps Oliver to become a new candidate for mayor and meets a new boyfriend Alex Davis. Damien Darhk's wife, Ruvé Adams, eventually brainwashes her boyfriend into kidnapping her to a miniaturized H.I.V.E. facility built from stolen technology belonging to Oliver's ally Ray Palmer.