Click on your profile picture at the top left of the screen to go to your profile, scroll down a little and you should see "account settings" towards the right hand side - click that, look over to the right on the next screen and you will see "other settings", under that click "ignored users", on the next screen type the user's name into the "Add new user to ignore list" box and it should come up with options for what you want to block.
It doesn't block posts, unfortunately, so if they regularly post, you will still see the titles.