U.S. Democratic presidential candidate Barack Obama, for the first time, introduced his selected running mate, Senator Joe Biden, at a rally in Illinois, on Saturday afternoon.

Before thousands of crowd in Springfield, Obama described Bidenas a "statesman with sound judgment who doesn't have to hide behind bluster to keep America strong."

US Democratic presidential candidate Barack Obama, for the first time, introduced his selected running mate, Senator Joe Biden, at a rally in Illinois, on August 23, 2008.[Xinhua]

Obama underscored Biden's accomplishments in the Senate in the past three decades, his background from a blue-collar family and his experience on foreign policy and national security as the Senate Foreign Relations Committee Chairman.

He also recalled the Biden's compelling story that his ex-wife and baby daughter were killed in a car accident just around he was sworn into the Senate, and he had to raise his remaining two sons on his own for five years.

"For decades, he has brought change to Washington, but Washington hasn't changed him," Obama said. "He's an expert on foreign policy whose heart and values are rooted firmly in the middle class."

It was the first time for the Delaware Senator to join in Obama's campaign. He hailed the Illinois Senator as a "leader who is ready to step in and be president," and he was proud to "stand firm with the next president of the United States of America, Barack Obama."

"Folks, we come from very different places, but we share a common story, an American story. He was the son of a single mom, a single mom that had to struggle to support her son and her kid," he said of his similarities with Obama's background.

"I was an Irish Catholic kid with a father like many of yours, in tough economic times and fell on hard times. But my mom and dad raised me to believe, my dad repeated it, it's not how many times you get knocked down. It's how quickly you get up," he recalled.