Seán Mac Diarmada (1883-1916) stands among the most dedicated and indispensable organisers of the Easter Rising. From his youth, he gave himself wholly to the cause of the Irish Republic, working through the Gaelic League, Sinn Féin and above all the Irish Republican Brotherhood. Though weakened by illness, his resolve never faltered and he became one of the chief architects of the conspiracy that prepared the Rising of 1916. Alongside Tom Clarke, he laboured patiently and secretly to bring together the forces that would strike for Irish freedom. His name stands among the seven signatories of the Proclamation, marking his place in the supreme act of national defiance. Executed by the British after the Rising, Mac Diarmada sealed a life of quiet discipline and sacrifice with martyrdom. In his organising genius, fidelity and unbroken commitment, he embodied the hidden strength behind the reassertion of the Irish freedom on the Easter Monday of 1916.