People

Paul Graham is a programmer, essayist, and Lisp expert who co-founded Y Combinator in 2005 after selling his startup Viaweb to Yahoo. He designed the batch-funding model and, through his widely read essays, supplied YC's intellectual framework and public credibility for its first decade.

Jessica Livingston is a writer and startup community organizer who co-founded Y Combinator in 2005 and ran much of its early operations and admissions. Often underweighted in the public telling, she built YC's culture and the founder-empathy that became its signature, and authored the interview book 'Founders at Work'.

Robert Tappan Morris is an MIT computer science professor and Paul Graham's former Viaweb co-founder, who helped found Y Combinator in 2005. He lent deep technical credibility to YC's early years while remaining a faculty member at MIT.

Trevor Blackwell is a robotics entrepreneur and AI researcher who co-founded Y Combinator in 2005 after earlier working with Paul Graham at Viaweb. Alongside YC he founded the robotics company Anybots, bringing a hardware and engineering perspective to the partnership.

Sam Altman went through YC's first batch as co-founder of Loopt, joined as a part-time partner in 2011, and became president in 2014 when Paul Graham stepped back. He scaled YC dramatically — larger batches, hard-tech bets, and the YC Continuity growth fund — turning the accelerator into a multi-stage capital platform.

Garry Tan is a designer-turned-investor who was an early YC partner and a co-founder of seed fund Initialized Capital before returning to lead Y Combinator as president and CEO in January 2023. He refocused YC on the early stage, wound down its Continuity growth fund, and grew the accelerator's emphasis on AI startups.

Michael Seibel co-founded Justin.tv (which became Twitch) and Socialcam, then joined Y Combinator as a partner and ran the core accelerator as its CEO from 2016 to 2024. He shaped much of YC's modern founder education and later returned to a hands-on group-partner role mentoring early-stage startups.

Paul Buchheit was Google's 23rd employee and the creator of Gmail before co-founding FriendFeed and joining Y Combinator as a partner in 2010. As one of YC's first partners beyond the founders, he advised startups for fifteen years before transitioning to Partner Emeritus in 2025.

Jared Friedman co-founded Scribd (YC 2006), which grew into one of the most-visited sites on the web, before joining Y Combinator as a partner. At YC he serves as Managing Director for software and is an active group partner and early-stage angel investor.

Dalton Caldwell is a music-tech entrepreneur who founded imeem (acquired by MySpace) and App.net before joining Y Combinator as a partner in 2013. As a managing director and group partner he has worked across more than twenty batches, advising over a thousand startups.

Diana Hu was co-founder and CTO of Escher Reality (YC S17), an augmented-reality backend company acquired by Niantic, the maker of Pokémon Go. She later joined Y Combinator as a group partner, bringing deep machine-learning and infrastructure expertise to early-stage technical founders.

Harj Taggar went through YC as co-founder of Auctomatic (YC W07), then in 2010 became the first partner hired from outside the founding group. He left in 2014 to start Triplebyte (YC S15) and rejoined YC in 2020, where he is a managing partner.

Geoff Ralston led the development of RocketMail (which became Yahoo Mail) and co-founded the edtech incubator Imagine K12 before joining Y Combinator as a partner in 2012. He served as YC's president from 2019 to 2022, steering the firm through the pandemic and fully online, record-sized batches.

Aaron Harris co-founded Tutorspree (YC S11) and joined Y Combinator as a partner in 2014, where he spent roughly seven and a half years. He worked closely on YC's investment processes and founder support, including helping run the Series A program for alumni.

Kevin Hale co-founded the online form builder Wufoo, one of the earliest YC-funded startups (acquired by SurveyMonkey in 2011), then became a Y Combinator partner from 2013 to 2020. He focused on user experience, product design, and customer support, helping founders refine their products.

Tom Blomfield is a British entrepreneur who co-founded GoCardless (YC S11) and later the app-based challenger bank Monzo, building two billion-dollar companies. He returned to Y Combinator first as a visiting group partner and became a full group partner in 2023, advising founders on both B2B and consumer startups.