Miel

Miel was a Colombian peddler who was affiliated with both Kazuhira Miller (back when he was still a freelance mercenary prior to joining the Militaires Sans Frontières) and the MSF led by Big Boss.

Biography
During the week that Kazuhira Miller, then a drill sergeant for a guerrilla group that had been wiped out during a battle with Big Boss and the MSF with himself as the sole survivor, was planning for a "contest" to see if he can go free or join MSF, Miller, planning on having Big Boss either join him or otherwise stay away from him, managed to get Miel to deliver a letter to his cream of the crop guerrillas as a trump card (who weren't present at the battle) against Big Boss. He delivered the letter to the guerillas, who responded with: "Understood, the operation was a go," with the signal to emerge being when he loudly declared speed shooting when it was nearing dark. Unknown to Miller, however, Miel had actually been affiliated with MSF and managed to show the letter to Big Boss the moment after he was tasked with delivering it, resulting in his guerrillas joining MSF as well.

Behind the scenes
Miel was a character who appeared in the drama tracks "Snake & Kaz (Encounter)" included in Metal Gear Solid: Peace Walker - Heiwa to Wahei no Blues.