Holden Karnofsky is a co-founder of effective altruism, and pioneered GiveWell.
He was the CEO of Open Philanthropy, but is currently on a leave of absence to work on AI Safety.
In May 2012, Karnofsky posted Thoughts on the Singularity Institute (SI), which became the most-upvoted article ever on Less Wrong. It offered a detailed critique of what is now the Machine Intelligence Research Institute, and spawned a great deal of discussion.
MIRI staff posted two replies:
Paul Crowley ("ciphergoth") posted discussion articles for each point raised: