The people mentioned on the Effective Altruism Wikipedia page:
Peter Singer: Professor of Bioethics (philosopher)
Toby Ord: Philosopher. Philosophy PhD, Computer Science bachelors
Hilary Greaves: Philosopher, and he double-majored in physics in undergrad
William MacAskill: Philosopher/Ethicist. PhD in philosophy.
Eliezer Yudkowsky: self-described autodidact, no formal education or notable work history. Runs a "AI" "Research" center called MIRI.
Holden Karnofsky: Co-Founder of GiveWell, Harvard degree in Social Studies
Yew-Kwang Ng: Welfare Economist, has published biology, mathematics, philosophy, cosmology, psychology, and sociology papers.
Derek Parfit: Philosopher. Has a history degree.
Nick Bostrom: Philosopher. BA in philosophy and math, MA in philosophy and physics.
Benjamin Todd: Physics/Philosophy double major, worked at Kodak for eight months and at an investment firm for 1.25 years before joining the Centre for Effective Altruism.
The financial backers are more diverse:
Dustin Moskovitz: Co-Founder of Facebook, Co-Founder of Open Philanthropy
Cari Tuna: Dustin's wife, previously worked as a reporter before cofounding Open Philanthropy
Dan Smith: Professional poker player
Liv Boeree: Professional poker player. Physics degree
Sam Bankman-Fried: con-artist, thief, fraudster. Has a physics degree and a minor in math, interned/worked as a trader at Jane Street, and founded Alameda Capital and FTX.