You can find real celebrities on Twitter (with the checkmark after their name).
But, you can also find dead celebrities, famous people and others created by someone with an interest in history or just having a lot of snark. I also follow a few who post from the point of view of people living in a specific period of time, like Victorian women.
If you have an interest in a particular celebrity or famous person try searching for the name on Twitter, see what comes up.
If you created a historical fictional account yourself, who or what time period would you mimic?
Historical Tweets – outdated database but still useful.