Meta CEO Mark Zuckerberg arrived at a Los Angeles court on Wednesday to testify at a groundbreaking social media addiction trial, where Instagram and other platforms are accused of deliberately hooking young users.

The 41-year-old head of Meta — which owns Facebook, Instagram and WhatsApp — is the most hotly anticipated witness in the California trial, the first in a series of cases that could set legal precedent for thousands of lawsuits filed by American families against social media platforms.

The trial will mark the first time the multibillionaire will address the safety of his world-dominating platforms directly before a jury.

Zuckerberg’s controversial reputation has loomed over the proceedings since jury selection, when Meta’s lawyers worked to exclude California residents deemed too hostile toward the Facebook founder.

The 12 jurors in Los Angeles will hear testimony until late March before deciding whether Google-owned YouTube and Meta’s Instagram bear responsibility for the mental health problems suffered by Kaley GM, a 20-year-old California resident who has been a heavy social media user since childhood.

Kaley GM started using YouTube at age six, Instagram at 11, then TikTok and Snapchat.