By Jim Forsyth

SAN ANTONIO (Reuters) - The selection of San Antonio Mayor Julian Castro as keynote speaker at the Democratic presidential nominating convention in September adds jet fuel to the lofty ambitions of a politician often labeled as the most promising Hispanic Democrat in the United States.

Castro, 37, has helped guide the transformation of San Antonio into the nation's seventh largest city with a healthy economy and a vibrant majority-Hispanic population.

"The mayor certainly reflects what's going on not just in Texas but across the country with the demographic changes," said San Antonio attorney and business consultant Joe Krier, an active Republican who worked closely with Castro as former President of the Greater San Antonio Chamber of Commerce.

"Mayor Castro is seen by many as a rising young star in the Democratic Party."

The choice of Castro as keynote speaker was strategic, as President Barack Obama needs the votes of Hispanics in swing states such as Colorado and Florida to win a second term.

Castro's life story rivals that of Republican Cuban-American star Marco Rubio, the Florida Senator thought to be on the vice presidential short list of presumptive Republican presidential candidate Mitt Romney.

Castro (who insists that his first name be pronounced the Latino "hoo-lee-AHN," and not the Anglo ‘JOO-lee-un'), learned politics early at the feet of his single mother Rosie, a leader of the fiery La Raza Unida nationalist Hispanic movement in the 1970s.

She was defeated as a candidate for the San Antonio City Council at a time when Hispanics were essentially shut out of the city's governing process. Rosie Castro saw to it that her twin sons Julian and Joaquin were both educated at Stanford University and Harvard Law School.

Julian Castro served on the San Antonio City Council for four years before becoming mayor.

Castro said he will detail in his keynote address how government "investments" helped him achieve the American dream.

"The choice that we have in this election is whether we will continue to make the right investments, that the American dream remains available to everyone," he said in an interview Tuesday. "I'll talk about how we will continue to have an opportunity to extend that promise to all Americans in the future." Continued...