A full back who can also play as wing back and a threat from set pieces, Marcos Alson was born in Madrid on 28 December 1990 and comes from a family with a strong footballing tradition. His great grandfather, Luís Zabala; his grandfather, Marcos Alonso Imaz, "Marquitos"; and his father, Marcos Alonso Peña; were all professional footballers. His father and great grandfather both did do for Barça.

Marcos Alonso started out at Atlético Madrid and was later at Real Madrid, making his debut on 4 April 2010 against Racing Santander.

However, Alonso has spent most of his playing career in England. After Bolton Wanderers he was at Fiorentina on loan from Sunderland, and then Chelsea came in for him.

He became a global superstar at Stamford Bridge, his biggest achievement being the Champions League title.

Marcos Alonso's debut season as a blaugrana saw him form part of a defence that conceded just 18 goals in 38 league matches on their way to the La Liga title, the second piece of silverware of the campaign after the victory over Real Madrid in the Spanish Super Cup final. 

Alonso is also a Spanish international, having made his debut against Argentina in 2018.