Carlos Spencer first came to the attention of Auckland boss Graham Henry while playing for Horowhenua in a Ranfurly Shield match against Henry's men in 1991. Spencer was headhunted by Auckland, beginning a long association between the man who would become known as 'King Carlos' and Auckland rugby. He played in the Blues' first-ever Super 12 game in 1996, and would go on to represent the team until 2005.
He made his first Test appearance for the All Blacks against Argentina in 1997, landing 33 points in a 93-8 win. He struggled to fight his way past Andrew Mehrtens into the All Blacks jersey on a regular basis, often finding himself on the bench until 2002.
Having been selected for the All Blacks' 1999 World Cup squad but not playing through injury, Spencer finally made his mark at the 2003 tournament in Australia. He will be remembered however for the loose pass that was intercepted for a try by Australia centre Stirling Mortlock, sending the All Blacks out at the quarter-final stage.
Having won the Super 12 with the Blues in 2003, Spencer moved to Northampton Saints in 2005, ruling himself out of contention to play for the All Blacks against the British and Irish Lions in order to train with his new club.
Spencer enjoyed a successful period with the Saints despite their relegation from the Premiership in 2007, becoming a senior and respected player as they fought their way out of National League One. Spencer left Northampton in January 2009 after failing to break into the first team on a regular basis following their return to the top flight.
He later signed for Premiership rivals Gloucester on a short-term deal, leaving them to return to Super 14 action with the Lions in 2010. He would eventually move into a coaching role with the Johannesburg-based franchise under fellow Kiwi John Mitchell.