Guards

Guards are normally your ally, as they protect the peace in the cities. However, some Guards are corrupt, and will attack you, forcing you to defend yourself. Also, if you are caught stealing or attacking people, the Guards will come after you, too!

Guards are usually found patrolling castles and cities, or something else of importance.

Evolution in the series
The Guards of Ultima I, II and III were hard to beat, but the only source of Lockpicks. In Ultima III, Guards could be bribed to leave you alone. In Ultima IV, Guards were weak, but attacking them wasn't a very good idea to further the game. In Ultima V and VI, guards were also armed with crossbows, and hard to beat. The Guards of Ultima VII were again easy, as are the ones in Ultima Underworld II.

The Guards of Pagan were a different breed. They were much tougher and did much more damage. Also they called Beren, which usually means death.

The Guards of Ultima IX were, per programming, unbeatable.