Why it matters: The board change comes amid growing scrutiny of Reddit's content moderation, which has often been accused of not curbing hateful content enough.
Notably, Siebel runs Y Combinator's accelerator program, which helped Reddit in its earliest days.
Siebel himself co-founded two companies that went through the program, Justin.tv which eventually became Twitch, and SocialCam, which he sold to Autodesk in 2012.