William Castillo Guardado

William Castillo Guardado joined the firm in 2023. He brings an analytical and thoughtful approach to litigation honed through years of experience in employment, business, and human rights matters.  

William’s practice currently focuses on all phases of litigation in antitrust and generative AI class actions. He represents book authors in the Databricks, Inc. Large Language Model Litigation and NVIDIA Large Language Model Litigation copyright class actions alleging that AI companies used pirated copies of books to train their large language models. He believes that AI companies have a responsibility to ethically obtain the training data for their models and compensate artists for use of their works. He also represents former employees of outpatient medical centers in Medical Center Employee No-Poach Litigation, alleging a no-poach agreement among certain companies to restrict the recruitment and hiring of employees.  

Previously, William was an attorney at a general civil litigation firm in the Bay Area, handling employment discrimination, business, and real estate litigation disputes in California federal and state courts.   

William was also an attorney at Catholic Charities Community Services in New York City, where he argued cases before the Second Circuit Court of Appeals and Board of Immigration Appeals. An advocate for pro bono services, he provided more than one hundred free legal consultations to members of the immigrant community in New York City and the Lower Hudson Valley. 

In 2014, William was based in Tajikistan in Central Asia as an attorney with the Danish Refugee Council and the Center for Gender & Refugee Studies. He represented refugees from Afghanistan in proceedings before the UN High Commissioner for Refugees, delivered humanitarian aid, and led field research on legal protections for women and children in Central Asia. William also traveled to Afghanistan for one week to deliver a training to lawyers on representing survivors of gender violence. 

During law school at UC Law San Francisco, William was a senior articles editor for the UC Law Journal of Race and Economic Justice, president of the Government Law Organization, and political chair of the La Raza Law Students Association.

William is Treasurer of the Association of Latino Marin Attorneys, and a member of the American Bar Association and the Bar Association of San Francisco.