Barack Obama made history Wednesday as he formally won the Democratic Party's nomination for president -- making him the first African American to lead a major party ticket.

Obama made a surprise speech on-stage in Denver at the DNC, his first on-stage appearance at the convention with VP running mate Sen. Joe Biden.

In his speech, the Democratic presidential nominee praised his wife Michelle for her DNC speech, saying she "kicked it off pretty well." Obama also commended former competitor Sen. Hillary Clinton.

"If I'm not mistaken, Hillary Clinton rocked the house down last night!" Obama told the enthusiastic crowd.

He also publicly thanked former President Bill Clinton for being "a president who actually puts people first."

Obama is expected to make a substantial speech Thursday night at the DNC, which he announced will be moved to Invesco Field at Mile High to accommodate a larger crowd.

To prepare for Thursday night, Obama is said to be looking at the nomination speeches of former Presidents Bill Clinton, Ronald Reagan and John F. Kennedy, the Associate Press reports.