Humoid Traders are NPCs that can sell items, and can be distinguished by the $ sign on their chests. They sell a wide variety and their stock seems to change daily (needs confirming). If you try to steal from them and are detected, they will attack you with weaponry. With no armour and at a low level they can kill you very quickly. They range in sizes and at bigger sizes they can be very deadly if aggravated. The larger sized traders normally sell stock with higher levels than the smaller traders. The Trader shown in the picture on the right is an example of a small trader. ------>
Humoid Leaders are NPC's that can give quests, items, and tell the storyline (will give you parts of main quests), and are distinguished by a star on their chests. Leaders are normally found in forts or buildings and will normally be in a seperate room to traders. They can sometimes be found in packs with Humoid Soldiers and Humoid Traders, going around and killing Neanders.
Humoid Soldiers are the other Humoid NPCs, and do not have distinguishing markings like the traders and leaders. The soldiers seem to come in an even wider array of sizes, and some of them will tower over your character in size. These soldiers will rarely be found in buildings, and can mostly be found roaming around outside, engaging any enemies they see. While you can't trade or get quests from them, you can use the F key when near them in order to try and convince them that you're a leader - if successful, they will follow you around and help out in combat, which is usually necessary to do against capital ships, but may not help against demons, as your allies could get in the way and hinder you from getting in close with a demon smiter.