A name for your character might be a clone, or a close clone. A clone is described in MW, 2nd meaning, as a copy or duplicate. TvTropes does call such a character a Captain Ersatz, as Emily Murphy points out.
"Clone" may be closer to the word you seek than ripoff, which is an intentional deception. The term knockoff is extensively used in the fashion industry; some knockoffs may be marketed as genuine and other may not.
Whether a comic book character that's copied from an existing character, or is heavily based on an existing character, violates a copyright isn't known when when the comic including the character is published (although a lawyer may be able to advise). Here's a paragraph from Wikipedia on a major case:
National Comics Publications v. Fawcett Publications, 191 F.2d 594 (2d Cir. 1951). was a decision by the United States Court of Appeals for the Second Circuit in a twelve-year legal battle between National Comics (also known as Detective Comics and DC Comics) and the Fawcett Comics division of Fawcett Publications, concerning Fawcett's Captain Marvel character being an infringement on the copyright of National's Superman comic book character. The litigation is notable as one of the longest-running legal battles in comic book publication history.