Paul Graham, a founder of the startup accelerator Y Combinator, is stepping down from his position as head of the program.

The startup ecosystem luminary announced the news today in a blog post, in which he named Sam Altman as YC’s new leader.

“Why the change? Because YC needs to grow, and I’m not the best person to grow it,” Graham wrote. “Sam is what YC needs at this stage in its evolution.”

Altman will take over as president starting with the next batch of startups going through YC. Graham will keep holding office hours.

Y Combinator started in 2005. It’s credited as a pioneer of startup accelerators.

Graham has found himself in the middle of debates about women in tech and startup founders with accents.

In 1995 Graham co-founded Viaweb, which he describes as “the first software as a service company” in the bio on his personal website. Yahoo bought Viaweb for $49 million in 1998.

Altman co-founded YC startup Loopt, which prepaid card company Green Dot bought for $43.4 million in 2012. He became Green Dot’s chief technology officer. He founded the seed-stage fund Hydrazine Capital, according to his YC bio.