Marcos Alonso Mendoza is a Spanish professional football player who currently plays as a left-back for Chelsea FC and the Spanish national team. He was born on December 28, 1990, in Madrid, Spain, and began his youth career at Real Madrid’s academy.

Alonso made his professional debut with Real Madrid’s B team in 2008 and later went on loan to Bolton Wanderers, where he made 20 appearances during the 2010-11 season. He then returned to Spain and played for several clubs, including Fiorentina, Sunderland, and Real Madrid again, before joining Chelsea in 2016.

Since joining Chelsea, Alonso has become an integral member of the team and has played a significant role in their success, including winning the Premier League title in 2017 and 2021, the FA Cup in 2018, and the Europa League in 2019. He has also been called up to the Spanish national team, earning his first cap in 2018.