denigrate

(verb) cause to seem less serious; play down. Synonyms: minimize, belittle, derogate. Example: "Don't belittle his influence."

(verb) charge falsely or with malicious intent; attack the good name and reputation of someone. Synonyms: defame, slander, smirch, asperse, calumniate, smear, sully, besmirch. Example: "The journalists have defamed me!" "the article in the paper sullied my reputation."