 Díaz's father, Rubén Díaz Sr., is a New York City Councilman who formerly served in the New York State Senate.Díaz was elected to the Assembly at the age of twenty-three, which made him the youngest person elected to the legislative body since Theodore Roosevelt.While in the Assembly, Díaz sponsored, co-sponsored and passed legislation addressing health care, public records access, minimum wage and overtime pay, environmental protection, equitable labor standards, insurance fraud, tenants rights, transparency and disclosure in all environmental impact statements, pedestrian safety, school bus safety, protection from tax preparers, Senior Citizens rights, wider access to the Senior Citizens Rent Increase Exemption (SCRIE) Program, and the regulation and accountability of gas and electric companies.