#1 Leo Messi
Of course, him.
Messi might be Argentine by birth, but he grew up at La Masia, moulded and shaped by the youth academy's Spanish footballing philosophies.
In the 2003/04 season, a ridiculously young 16 year old Messi rose through the ranks and made his debut for a record 5 teams. He'd made only over 20 appearances for the reserves when Frank Rijkaard, who had called him an "alien" and stated that even the senior team defenders were afraid to face him, promoted him to the first team in 2004.
It took him a while to get settled in, becoming a regular only in 2006. His friendship with Ronaldinho was helpful, and even today, you can see a few characteristics of the Brazilian reflected in Messi's style of play.
In 14 seasons, he's scored 530 goals in 612 appearances. Messi's been involved in every single bit of success that the Catalans have enjoyed over the last 15 years.
While Barca might be known for their teamwork and intricate play, Messi has carried both his team and his country on his own shoulders several times. He's done things that no other player would even dare try, he's scored goals and provided assists that defy imagination.
Its fair to say that Messi is not just Barcelona's best, he's probably the greatest of all time to have graced the beautiful game.