Then Illinois State Senator Barack Obama gave the keynote address at the 2004 Democratic Convention in Boston, MA. He was supporting Senator John Kerry's (D-MA) bid for the presidency, which was eventually unsuccessful. Kerry lost to incumbent President George W. Bush. That same November, Obama defeated Alan Keyes to become Illinois' U.S. Senator.
In the end, Obama's speech set the stage for his own winning presidential bid just a little more than four years later.
Related: Barack Obama's 2004 DNC Speech - Complete Text