He was part of a Spanish revolution, and is still very much loved at Anfield.
In his first few games at the heart of the midfield, jaws dropped at Anfield for the pinpoint accuracy at which he could spray the ball around the park - at times hitting his target without even needing to look, and there were the occasions where he would get the better of the opposition goalkeeper from his own half.
Alonso was signed by the Reds in 2004 from Real Sociedad for £10.7 million as one of the first signings of the Rafa Benitez reign - his impact was immediate as he formed a key part of the Liverpool midfield. He was unfortunate to be on the wrong end of a tackle from Chelsea's Frank Lampard in the middle of his first season that kept him sidelined for around three months with a broken ankle. That season he would return to the side for the second leg of their Champions League quarter-final against Juventus where he controlled proceedings as the Reds put in a sterling performance to get a 0-0 draw.
He would end up missing the second leg of the semi-final against Chelsea that season through suspension but everybody remembers his contribution in the final in Istanbul as he followed up his own penalty - which was saved by Dida - to bring Liverpool level after being 3-0 down as Liverpool completed their greatest triumph.
He went on to win the FA Cup with the Reds the following season in similarly dramatic circumstances against West Ham, and played a role as Liverpool made it to another Champions League final in Athens in 2007.
In 2008 there was speculation he may leave the club after reports that Rafa Benitez wanted to sign Gareth Barry. That transfer didn't happen, and Alonso remained at the club for one more season. Some would say it was his best individual season at the club as he was at the heart of the midfield as Liverpool finished runners-up to Manchester United, with a Premier League record points total of 86.
He would leave in the summer of 2009 after scoring 19 goals from 201 games for Real Madrid for around £30 million. Silverware was inevitable for Alonso at the Bernabeu winning the La Liga title, the Copa Del Rey on two occasions, as well as being part of the squad that won Real's historic 10th European Cup.
In 2014 he moved on to Bayern Munich where he currently plays and has enjoyed further success where he has one Bundesliga title to his name so far.
His international career has also seen him win the European Championship's twice, as well as the World Cup with Spain.