Teague Martin is an Overseer of the Abbey of the Everyman, who became an agent for the Loyalists and was instrumental in breaking Corvo Attano out of Coldridge Prison. He was discovered by his fellow Overseers and captured, but was able to escape with Corvo’s assistance.
Martin’s ultimate fate is based on Corvo’s chaos level. In low chaos, Martin is found dead at a large table along with Pendleton during Corvo’s final mission, presumably poisoned by Havelock.
In high chaos, Martin can be found in front of the Kingsparrow Fort gatehouse attempting to reach Burrows Lighthouse.
When confronting him, Martin will hold a pistol to his head, but if you kill him before he shoots you get a special kill animation.