Riley Costello is a fictional character from the British Channel 4 soap opera Hollyoaks, played by Rob Norbury. Riley was introduced in July 2010 with his on-screen family as part of a cast overhaul of the series. In December 2011, the serial's executive producer Emma Smithwick said that Riley would remain in Hollyoaks despite his family's departure.

In 2010, auditions were held for the part of Riley, a young footballer and member of the Costello clan. Former Grange Hill and Hollyoaks: In the City actor Rob Norbury was cast in the role. The Costellos were introduced as the family of already-established character Jem Costello (Helen Russell-Clark). The family consists of Carl Costello (Paul Opacic), a former premiership footballer with a history for cheating on his wife, Heidi (Kim Tiddy), a former model, and their children, Riley, who is training to become a footballer to impress his father, Seth (Miles Higson), who is desperate to step out from his older brother's shadow, and Jasmine (Victoria Akin), who is secretly suffering gender identity disorder. Speaking of the family's casting, Marquess said, "We can't wait for this huge new boost of energy exploding on screen. These exciting new characters join our fantastic core cast. Together they will ensure that 2010 will be a year to remember on Hollyoaks."

Mercedes Fisher (née McQueen; previously Owen) is a fictional character from the British Channel 4 soap opera Hollyoaks, played by Jennifer Metcalfe. She debuted on-screen during the episode airing on 19 June 2006 as the first character to be introduced to the serial by series producer, Bryan Kirkwood. In 2008 Metcalfe feared that the character was to be axed but was later reassured by the series producer that she wouldn't be. Metcalfe later stated her itention to stay with the serial. Mercedes is part of the McQueen family and is the longest serving McQueen on the serial.

Mercedes is described as a "savvy, ballsy girl that can't say no and is unapologetic about it". She is played as a having moments of happiness which she ruins for herself and as managing to justify "whatever she does that's bad". Throughout her time on the serial Mercedes storylines have centred on her relationships. These include her marriages to Russ Owen (Stuart Manning) and Malachy Fisher (Glen Wallace), the latter saw her involved in an HIV storyline, and an engagement to Riley Costello (Rob Norbury). She has also been central to several affairs which included Calvin Valentine (Ricky Whittle), her sister's husband, and Riley's father Carl (Paul Opacic). Most recently she was at the centre of a kidnapping storyline when she was held against her will by serial killer Silas Blissett (Jeff Rawle) before going into labour, giving birth to a boy as a result of the stress and more recently prostitution.