Throughout your play of Rimworld you will come across several different types of characters. Some of these characters will be friendly such as drifters who just wander through your colony and other hostile, such as the mechanoids, looking to destroy you.
As of Alpha 14 (July 15th, 2016), traders, visitors, raiders, kidnappers, animals, etc will now escape if surrounded by walls with no way out.
As of Alpha 16 (December 20th, 2016), rescued people (especially space refugees etc) should sometimes join the colony. If the environment isn’t survivable (e.g. bad temperature, toxic fallout) they should always join the colony.
Main Article: Animals
Wild animals occasionally spawn on the map according to the biome and from random events. These wild animals and tamed animals will wander and graze on vegetation, including player-grown plants, regardless of type. Growing food outdoors can sometimes attract animals to your base perimeter. Animals are an important source of food by the meat they provide once hunted and butchered.
Raiders will target tamed animals as often as colonists.
As of Alpha 14 (July 15th, 2016), animal trainers receive 90 XP per training attempt, which is increased from 60 in Alpha 13. Taming an animal also grants 90 XP per attempt, which previously did not occur. When animals nuzzle a colonist, it counts as a social interaction and is logged in the social tab of both the colonist and animal.
Main Article: Colonists
Colonists are the living inhabitants of each RimWorld colony. Each colonist has specific skills, positive and negative traits, and a character backstory. In general, every human is a colonist except for raiders/travelers/prisoners. The colonists come in various outfits based on their background, which can be seen by looking at the 'Character' tab in game.
Main Article: Mechanoids
"Mechanoids - Autonomous intelligent robots built for domestic, industrial or military purposes. Only available to advanced cultures because such complex AI is needed to control them."—RimWorld Universe Quick Primer
Main Article: Prisoners
Prisoners are people, usually raiders, hostile tribals, or your own colonists undergoing a mental break, who have been taken captive. They are unable to leave their prison barracks and can only use facilities (such as a food dispenser or shelf) on their own if they are placed inside the prison barracks.
You should notice that your colonists won't haul food away from cells, even when directed to do so. Animals may still enter the cell on their own and eat that food however.
Main Article: Raider
Raiders are enemies that spawn in groups at semi-regular intervals. Group size, health, skill, and equipment depend on both the set game difficulty and the time already elapsed in the game. Typically on Tough Cassandra Classic only one wounded raider spawns in the first group. The subsequent group has 3-5 raiders, and eventually, there are groups of more than 20 raiders with the lowest health being above 80. Raiders will invoke a message when they spawn, and an alert will come when they begin their assault.
Raiders can enter "steal" mode if they see enough valued objects lying around. In this mode, they will grab your stuff and carry it off.
When they damage your colony enough, they may also be satisfied with the damage done and will decide to leave.
Alternatively, if there are downed colonists within reach, they may try and kidnap them by letting some do the actual kidnapping and some covering them. After one of your colonists has been kidnapped, a ‘ransom demand’ incident can fire, demanding silver for the colonists that has been kidnapped.
If half of the members of a humanlike raid has been killed or downed, the rest will flee in panic, where they will run as fast as they can to the edges of the map, and will not fight back, even if they are attacked.
Pirates or Outlanders can spawn with both ranged or melee weapons, all melee with personal shields, or all ranged.
Tribals usually come in a mix of ranged and melee warriors.
Raiders will attack randomly chosen constructed objects or colonists. They will not attack natural rock walls (not the case for sappers, animals (unless the animals are hostile or tamed) or unpowered turrets. They will also engage prisoners that are from an enemy faction.
Raiders will usually set fire to crops in growing zones, power generation or conduits, walls, nutrient paste dispensers, shelves, orbital trade beacons; they will melee-attack lamps, beds, stools, short tables, long tables, and doors; they also use molotovs and frag grenades on turretss, sandbags, or other targets, and some use EMP grenades to stun your turrets.
As of Alpha 15 (August 28st, 2016), raiders steal a bit more often now.
As of Alpha 17 (May 24th, 2017), raiders won't compulsively attack doors.
Occasionally an event is triggered that spawns a group visitors from a friendly faction at the edge of the map that comes and mills about the colony. Sometimes one member of the group has items to trade, indicated by a question mark over the pawn. To initiate trade, select a colonist and right-click the trader.
A visiting group's arrival could prove advantageous if the colony is assaulted by a mutual enemy while they are present. See Events - Faction visit.
When leaving, visitors will carry away wounded members of their faction.