Girls Aloud were formed on November 30, 2002, in front of millions of viewers on the ITV1 programme Popstars: The Rivals. The concept of the programme was to produce a boyband and a girlband who would be 'rivals', and battle it out for Christmas #1 2002. Following the success of Hear'Say (winners of the original Popstars show), several thousand applicants attended auditions around the UK, hoping for a place in one of the groups. Thousands were narrowed down to just ten men and ten women chosen as finalists by judges Pete Waterman, Louis Walsh and Geri Halliwell. However two finalists were disqualified before the live shows started: Hazel Kaneswaren was found to be too old to participate, whilst Nicola Ward refused to sign the contract, claiming the pay the band would go on to receive was too poor. Two new finalists (Kimberley Walsh and Nicola Roberts) were chosen as their replacements.

During October and November, the finalists took to the stage participating in week-by-week live performances every saturday night (alternating between the girls & boys each week). One contestant was eliminated each week (due to polling the least amount of phone votes) until the final line-ups of the boy band and girl band emerged. The 5 girls who polled enough votes to make it into the band were Cheryl Tweedy, Nadine Coyle, Kimberley Walsh, Nicola Roberts and Sarah Harding. They called themselves Girls Aloud and were managed by Louis Walsh (and Hilary Shaw from 2005). The winning boy band was called One True Voice and was managed by Pete Waterman.

In Christmas 2002 the two bands competed for the symbolic number one position in the Christmas Week UK's singles chart. Girls Aloud won the battle with their single Sound of the Underground (produced by Brian Higgins and Xenomania) which stayed at number one for four weeks. Disney Channel viewers later voted this as best single of 2002-2003 at the Disney Channel Kids Awards. Originally tipped to be more successful than the girls, One True Voice released just two singles, achieved little success and quickly disbanded.

--Wikipedia