Yoki is, when first introduced, a corrupt member of the military who imposes heavy taxes on the town of Youswell, bankrupting its citizens. When the Elric brothers arrive in town, they trick Yoki into giving up ownership of the town and promptly report his actions to the military He is stripped of his rank and lives as a homeless person on the outskirts of Central, where he meets the fugitive Scar. In the anime, Yoki alerts the military to Scar's location, and in the subsequent raid to apprehend Scar he is killed by Lust. In the manga, Yoki is forced to work for Scar under the threat of death. Though he tries to convince those they encounter that Scar is his servant, Yoki does as Scar commands and calls him "master". Since he has started following Scar around the country, Yoki has assumed a role as comic relief, often having pain inflicted upon him when he tries to seem superior to others.

-Wikipedia