I am going to mention one sire that I've had a lot of experience with, although I'm sure there are many out there that I am not familiar with. He is an (1995 birth date) old bull, AAR Really Windy 1205. I've raised over 200 head of cows over about a twelve year period from him, and sold many bulls sired by him as well. Generally, the disposition is extremely gentle, although (as with about any sire) there have been a few exceptions.
However, the bull is only half of the disposition, and possibly even less than that. The dam's sire as a group can have a lot of influence on disposition, as well as the individual animal.
The second thing, and I agree with the posts that have mentioned this, is the way the cattle are handled and managed. It is amazing, but there are some people out there who just seem to make cattle nervous. I've worked with some producers that are the same way. I usually help them one time, and then make excuses not to help the next time, if it is a "rodeo approach" to working cattle. I hope that helps.