Sebastian is often seen standing outside the Church of Scientology Information Centre, with information pamphlets in hand and a big smile on his face.
He's unwittingly become the adored face of Scientology, ironically thrust into the limelight by a group of protestors who have camped outside the Scientology centre to "raise awareness" of the group's alleged dark past and myriad transgressions.
Watch the trailer for Louis Theroux's My Scientology Movie, a deep dive into the church. Post continues below.
In an in-depth Rolling Stone feature on the Scientology protests, a source formerly close to the church believes Sebastian is most likely what's known as a "body router" - aka an attractive young staffer tasked with inviting passersby to learn more about the church.
"Look at that smile, he has the best smile in the world," one protestor is heard saying in footage from the protests, which has been viewed nearly 18 million times on TikTok.
Sebastian the TikTok sensation.
"We love you, Sebastian. We just don't love the cult that you're in," another protestor says.
The fact that Sebastian has become a phenomenon on TikTok could cause problems for him with his church, according to former third-generation Scientologist Liz Gale. "Whatever he does is going to reflect on Scientology," she says. "So they're going to put as much control on him as possible."