In Anno 1800 you can meet many different characters. The computer players are divided into four different groups. In the first group there are the so-called AI opponents. These are the ones that populate different islands to build empires just as you do. In the second group there are the neutral traders. These are characters who already own a small special island at the beginning and don't expand to other islands. They trade with all players, you cannot change your diplomatic status with them. In the third group there are the pirates. They too already have a small island at the beginning of the game and don't expand to other islands. Pirates are hostile and aggressive, they attack all players' ships and islands. There are also some other characters who don't play a big gameplay role but appear in the campaign or inform players about various events.
Each one of the AI opponents has its own personality which affects not only the general difficulty rating but also influences their playstyle. AI Opponents are divided into three difficulties: easy, medium and hard.
See each individual computer player's page for more details.
Dr. Hugo Mercier (DLC)
Main page: Neutral Traders
Unlike AI opponents, they are neither direct allies nor opponents, but they are an important part of the game world's atmosphere. Four dealers are ready to provide you with goods, quests and items. Deeper diplomacy is not possible with them, they always have trade agreements with all players, it cannot be changed. The merchants regularly send out trade ships to buy and sell goods directly in players' ports. Each of them has their own preferences regarding supply and demand. Except for Sir Archibald Blake, you can disable all dealers before the game starts. Specific traders can be found only in a specific region.
Cape Trelawney (DLC)
Main page: Pirates
There are two neutral pirate leaders, one in the Old World and one in the New World. The Buccaneers can also be your potential allies. We rise in their favour when we win naval battles with other players. Then we can make peace with them, trade or even make alliances. They sell goods, items and ships, they can also offer you quests. If you are lucky you can even buy some special ships, which otherwise would require a specialist to build. Before the game starts, you can set their difficulty separately or disable them completely.
There are also other characters who don't fall into specific category and have little impact on the gameplay. They either appear in the campaign (like Hannah Goode) or inform the player about different game features or their progress (like Visitor informing about the activity of Public Mooring and the specialists randomly coming through visits.).