(Reuters) - If Neymar and his Brazil team mates are to reach the World Cup quarter-finals they will first have to slip past a guard dog at the heart of the Chile defense.

Gary Medel is known in his homeland as "Pitbull". He has earned his reputation with a series of uncompromising performances in defense and midfield.

Medel has been arguably Chile's best defender at the finals and appears to have put behind him a poor disciplinary record, which earned him 13 red cards in his early years.

He kept Spain forward Diego Costa under wraps in the 2-0 win over the holders in the group stage and will be key to Chile's chances of beating Brazil in their last 16 clash in Belo Horizonte on Saturday.

It is a repeat of their clash at the same stage of the last World Cup, when Brazil crushed Chile's emerging young side 3-0.

"This team is much more mature, especially me," the 26-year-old Medel told reporters recently at Chile's World Cup training camp. "I've now gone over a year without a red card."

Medel grew up in one of Santiago's toughest neighborhoods and believes football was his lifeline. "For my own sake, it's a good job that I chose football," he once said. "If not, perhaps I'd be stealing or drug trafficking."

He came to prominence at the 2007 Under-20 World Cup in Canada, where Chile finished third. The following year he made his debut in the World Cup qualifiers, scoring both goals in a 2-0 victory over Bolivia.

But in 2009 his life started to unravel when he was involved in a serious car crash.

VEHICLE WRECKAGE

Recalling the incident later, Medel said that as he sat slumped in the wreckage of his vehicle he could not feel his legs and feared he was paralyzed from the waist down.

A month later, a teenage girl fell to her death from the ninth-floor balcony of his apartment. An investigation cleared him of wrongdoing but the incident cast a shadow over him.

Wisely, he moved to Argentina, writing his own chapter in the history of Boca Juniors by scoring both goals in a 2-0 defeat of arch-rivals River Plate.

From there he went to Sevilla and on to Cardiff City in the English Premier League. Cardiff's relegation has raised speculation that Medel will move again after the World Cup.

By his own admission, Pitbull is a talker. An amusing video has emerged of him locked in a protracted war of words with Arjen Robben during Chile's group match against the Dutch, which they lost 2-0.

It is all good natured enough, and both players are smiling, but it is a reminder that Medel is prepared to stand up to any opponent.

Like a lot of Chile's players, he is covered in tattoos, including one of a pitbull terrier on his left shoulder.

One on his neck it says simply "Destiny". Medel and his team mates hope to write theirs against Brazil on Saturday.