Is this a good thesis on Frederick Douglass for my research paper? Frederick Douglass, one of the most significant abolitionist speakers, greatly...

I think it's a
great example of an intro thesis sentence, especially for AP US History if that's the class
you're in.  I think you could use a clarifying sentence, to hammer the message home.  Something
that argues the same point in a slightly different way sdo the reader knows without doubt what
the thesis is.