The "Big Fella". Michael Collins.

De Valera threw him under the bus by not conducting negotiations himself. Collins was threatened by Lloyd George with a resumption of a vicious and overwhelming campaign by British Troops unless he signed. Collins was faced with a choice of war or partition. DeValera was able to distance himself from the decision ( even though it was him who sent Collins to London to negotiate) by saying it wasn't him that agreed to partition. This single event led to the "troubles" 30 years later. N.I. became a "protestant state for a protestant people". Catholics couldn't vote (properly). Couldn't get jobs as businesses were owned by Protestant/Unionists. Civil rights marches started. These were crushed by army and Unionist militias. IRA was reformed to defend Catholic areas and so the madness started. Less than 9 months after signing , Collins, who was Chief of Staff (General) of Irish Free Stata Army, was killed in an ambush in West Cork.