A "shameless liar" is someone who tells falsehoods without any sense of regret or concern about the impact on others. There are several synonyms for this term that capture the same negative connotation. One option is "pathological liar," which implies that the person has a compulsion to lie even when there is no apparent benefit to doing so. Another synonym is "deceitful charlatan," which suggests that the person uses lies to defraud or manipulate others. "Mendacious schemer" is another option, highlighting the intentional and strategic nature of the dishonesty. Ultimately, regardless of the specific term used, a shameless liar is someone who cannot be trusted and should be approached with caution.