Number One
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Brother Cavil is a priest who provides counsel for Chief Tyrol (Lay Down Your Burdens, Part I) after Tyrol's maddened attack against Cally. Cavil identifies the source of Tyrol's anxiety as arising from the fear that he could be a Cylon agent, awaiting activation.
A somewhat eccentric figure, Cavil is a surprisingly harsh critic of prayer for a priest, but claims to have been preaching "longer than you [Tyrol] have been sucking down oxygen."
Cavil is portrayed by Quantum Leap's Dean Stockwell.