In Avot we learn that one should judge all people favorably ("והוי דן את כל האדם לכף זכות"). I would like to know if that includes the deceased. Meaning, can I look back on the life of a person who is now dead and, in reviewing his actions, judge them any which why I choose? Or, would the precept of judging favorably still apply?
Well, there's a חֵרֶם קַדְמוֹנִים to talk badly about the deceased.
As the Chafetz Chaim writes in הלכות אסורי לשון הרע - כלל ח
So if you wrongly accuse the deceased about something, you are the subject of an ancient excommunication.
That would be a strong impetus to judge them favorably.
Or, as the popular expression goes:
(Explanation: After they died they are Holy; a play on words of the 2 Parshiot Acharie-mot and Kedoshim.)