Holden Karnofsky — Notable For: Co-founder of GiveWell and Open Philanthropy; influential figure in effective altruism; author of 'Most Important Century' blog series on transformative AI

Note: The source text confirms the first part of the claim about co-founding GiveWell and Open Philanthropy. However, the provided excerpt does not address whether Karnofsky is an 'influential figure in effective altruism' or whether he authored the 'Most Important Century' blog series on transformative AI. These aspects are unverifiable from the given source text, making this a partial confirmation rather than a full confirmation.