SPRINGFIELD, Illinois (CNN) -- Presumptive Democratic presidential nominee Barack Obama introduced Sen. Joe Biden to the nation as his running mate Saturday, telling supporters that he is "a leader who is ready to step in and be president."
"For months, I've searched for a leader to finish this journey alongside me and join me in making Washington work for the American people. I searched for a leader who understood the rising costs confronting working people and will always put their dreams first," Obama said.
"Today, I've come back to Springfield to tell you I've found that leader," he said.
The rally is the pair's first joint appearance since Obama announced that Biden, the senior U.S. senator from Delaware, would be his running mate on his Web site and in a text message to supporters early Saturday morning.
Democrats hope that Biden's working-class roots and foreign policy experience will help Obama, who informed Biden of his decision Thursday.
Thousands of cheering supporters gathered Saturday for the rally in Springfield, Illinois, where Obama announced his candidacy last year. It will be their only public appearance together before next week's Democratic convention in Denver.
As he took to the podium at Saturday's rally, Biden invoked the 16th U.S. president, Abraham Lincoln, who was from Illinois.
"President Lincoln once instructed us to be sure to put your feet in the right place and then stand firm," said Biden, a native of Scranton, Pennsylvania.
"Today in Springfield, I know my feet are in the right place, and I'm proud to stand firm with the next president of the United States of America, Barack Obama."
Obama stressed those roots, introducing 65-year-old Biden as "still that scrappy kid from Scranton who beat the odds."
He noted hardships in Biden's life, including the deaths of Biden's first wife and infant daughter in a 1972 car wreck and his struggle to overcome a brain aneurysm in 1988. iReport.com: iReporters ask i...