Julian Castro was born in San Antonio, Texas, to Maria "Rosie" Castro and Jessie Guzman. He is the identical twin brother of current United States Representative Joaquín Castro. His mother was a Chicana political activist who helped start the Chicano political party, La Raza Unida. She also ran for the San Antonio City Council in 1971, but she did not win. Castro once said, "My mother is probably the biggest reason that my brother and I are in public service. Growing up, she would take us to a lot of rallies and organizational meetings and other things that are very boring for an 8-, 9-, 10-year-old".