The mysterious man is from Geneva, and, as the other commenter noted, we do not learn his name until a few chapters in. When he first begins to tell his story, which Walton transcribes and sends to his sister, Mrs. Saville, he says that his family was quite distinguished in their home republic. His father was a well-respected public figure for a great many years, and his mother was intelligent and brave, taking care of her own father, alone and in decline, for some months before her rescue by the man's father. The man says that "No creature could have more tender parents than mine." Eventually, his orphaned cousin, Elizabeth, was invited to come and live with his family, and they became complementary playmates. This man, as a child, wanted to discover; Elizabeth, and his best friend Henry, wanted to imagine. He was philosophical while they were passionate and romantic. He looks on his background with fondness, as though it were a time of innocence that preceded the sad events that have brought him to the North Pole.
One can assume, from the question, that the "man" referred to is found in the four opening letters of Mary Shelley's Frankenstein. Given that Walton only refers to the man as "the man" or "the stranger," readers are not directly told who the man Walton has found is.
Once the narrative is "given over" to the man (in all actuality, Walton is the sole narrator of the novel--telling the tale of Victor and of Victor telling the creature's tale), readers are only then told that the character is Victor.
Chapter one opens with the stranger telling Walton about the history of his family and their Genevese background. In reality, it is not until chapter three where the name Frankenstein is actually used: "So much has been done, exclaimed the soul of Frankenstein."