Archbishop Stephen Langton (c. 1150–1228) was a leading mediator in the barons’ dispute with King John and in the negotiations at Runnymede.
Following the death of Archbishop Hubert Walter in 1205, there was a prolonged dispute between King John, the monks of Christ Church, Canterbury, and Pope Innocent III over who should succeed him. Stephen Langton was eventually elected Archbishop of Canterbury by the monks of Christ Church in December 1206, and he was consecrated by the Pope in 1207. However, John continued to refuse to accept him, and Langton was not installed at Canterbury until 1213 when the King finally made peace with the Pope.
The first clause in Magna Carta confirmed ‘that the English Church shall be free and shall have its rights undiminished and its liberties unimpaired’, doubtless reflecting Langton’s influence. It may also be thanks to him that the Articles of the Barons has survived, since Langton apparently took this document away for safe-keeping after the meeting at Runnymede.
Further information about the life of Archbishop Stephen Langton can be found here via the Oxford Dictionary of National Biography.