But he names others who influenced him on the way as well: Bobby Kennedy, César Chávez, and controversial former San Antonio Mayor Henry Cisneros. Castro counts Cisneros as a trusted friend and says that his promise inspired him as a kid growing up in San Antonio in the 1980s and 1990s. "He did such a good job as mayor of the city, the first Latino elected of a major American city, that was very exciting back then," Castro said.
(Full disclosure: Cisneros serves on the board of directors of Univision, having previously served as CEO). After Julián left San Antonio, he was bitten by the political bug. During law school, Castro already had his sights set on winning a city council seat in his hometown. He held a fundraiser and collected $2,000 from his classmates for his campaign during his final year at Harvard, the San Antonio Express-News reported in 2009.
The other driving force in Julián Castro's life is his twin brother Joaquín, who is younger than the mayor by exactly one minute. Joaquín has a budding political career of his own. He has served as a state representative since 2002, but is now running for Congress. The younger Castro is likely to win his race in November; it is in a safe Democratic district.
As children, the two shared a bedroom and a healthy sibling rivalry. Julían said that during his childhood, he rooted for the NFL's Philadelphia Eagles simply because his brother was a fan of the Dallas Cowboys.
"Growing up, we were very competitive. We were actually competitive in school, competitive in sports. He was a little bit better in school, and I was a little bit better in sports," Joaquín said.
Always pushing each other to compete, Julían says that his brother helped him become the person he is today.
"In the end, the, the result of that was that we became better at both [school and sports]," he said. "So, I was really fortunate in that sense that that we had a good upbringing."
While Castro may have gotten his political inspiration from his activist mother, his style is much more Ivy League.
"My mother came up when there were definitely very, very many reasons to try and get out there and protest and to try and beat the door down," he said. "But one of the blessings of my generation is that their struggles have helped move America forward and we're the beneficiaries of that."
While he comes across as friendly, he has a quiet, analytical persona; the opposite of another prominent Latino politician — Rep. Luis Gutierrez (D-Ill.) — who still likes to "beat the door down."
In that sense, Castro is like Obama as well, a minority politician who also has appeal beyond his own community. "The destiny of the Latino community is interwoven with the destiny of the United States," he said.
When asked about what's the best way for members of the Latino community to combat Arizona-style immigration laws, Castro gives a pragmatic response rather than an emotional one. Instead of getting angry and demonstrating, "the best way to address that is to participate in the democratic process," he says.