Scott Alexander (Scott Alexander Siskind) is a psychiatrist and writer on the US West Coast best known for his blogs Slate Star Codex and its Substack successor Astral Codex Ten, where he writes long-form essays on reasoning, science, psychiatry, ethics, politics, and effective altruism. His blogs have become central venues for the rationalist and EA communities, and he has been widely cited and discussed in those circles. Clinically, he has practiced psychiatry at Lorien Psychiatry and previously at other US institutions, with a focus on treatment-resistant depression and related areas.