pathological liar

liar

is a person so addicted to falsehood that he can't tell the truth without lying.

A pathological liar is a person so addicted to falsehood that he can't tell the truth without lying.

is one who can always be expected to tell you where the truth lies.

A pathological liar can always be expected to tell you where the truth lies.

is one who has a minimum capacity for veracity or a maximum capacity for mendacity.

A pathological liar has a minimum capacity for veracity or a maximum capacity for mendacity.