Thomas Carlyle (1795-1881) was a Scottish Victorian essayist and satirist. He's most famous for calling economics "the dismal science."
Sartor Resartus is the work most likely to appear on the GRE Literature Exam.
Sartor Resartus (Latin, meaning roughly "The Tailor Re-tailored" or "The Tailor Re-clothed") is intentionally difficult to classify: it flits between satire and serious philosophy, between fact and fiction. The word was published in Boston with a preface by Emerson, where the work had a major effect on Transcendentalism.
For the exam, it's usually enough to be able to recognize the following characters and keywords as belonging to Carlyle's Sartor Resartus:
-Diogenes Teufelsdröckh (Latin, "God-born," and German, "Devil-shit")
-The Wanderer (another name for Teufelsdröckh)
-The Everlasting Yea (roughly, spiritual faith)
-The Everlasting No (roughly, spiritual doubt or cynicism)
-Weissnichtwo (Teufelsdröckh's hometown; German, "know not where")
If you want to go deeper, I recommend the Oxford World's Classics Edition.