Civilian unit for expanding your empire.
The Settler is used to found a new city. All civilizations and city-states begin the game with at least one Settler, but city-states (and Venice) cannot produce Settlers. Settlers cannot defend themselves, and are easily captured unless protected by a combat unit (which can be stationed in the same tile as the Settler).
Settlers consume all surplus Food in the city while they are being produced, effectively halting population growth; "stagnation" is displayed in place of the number of turns until a new Citizen is born. A portion of the consumed surplus Food is converted into Production towards the Settler. The portion of surplus Food that is converted into Production is significantly reduced beyond the fourth Food. This conversion process helps to reduce the negative impact of Settler production in cities with more excess Food, so that it is not always most efficient to produce a Settler in a city with the most Production and least excess Food.
A civilization may only acquire a Settler by producing or purchasing one themselves; a Settler captured by a different civilization immediately becomes a Worker. A city must have at least 2 Citizens before it can produce Settlers. In Gods & Kings and Brave New World, Settlers can be purchased using Gold.
Pioneers drive civilization. While most are satisfied with the status quo, happy just to survive, in every culture there are a few hardy individuals willing to strike out on their own, to risk everything in the hope of finding a better life for themselves and their children. In the past, brave settlers have led humanity out of Africa and into Europe, Asia, the Pacific, and the Americas. In the future they may lead the way to the moon, Mars, and even beyond.