Obtaining a highest fame rating requires that you simply use a character that is of that nature, or by completing skirmishes that reward that type of fame. There is also an option to take jobs from your lord if you're an officer which reward additional fame of different variations. Each of these fames can go as high as fame 9, so you'll have to take part in many battles before unlocking each respective trophy.
It is advised you only do one of these fame choices per playthrough, as there are trophies also tied for seeing endings which are determined by your highest fame.
There aren't very many solid evil characters, therefore I suggest you create your own and select the evil fame type for them using a style you enjoy. This way, you get the fame you are looking for as well as using a style that suits you.