Complex sentence: As a teenager, he developed a reputation as a prolific liar, given to telling fantastic tales about his family and personal life; he was also adept at changing his appearance according to what he felt was most attractive at a given moment.
Split into simpler sentences: As a teenager, he developed a reputation as a prolific liar given to telling fantastic tales about his family and personal life. He was also adept at changing his appearance according to what he felt was most attractive at a given moment.