expression
Used with verbs of giving, telling, showing, etc., to mean the action is directed toward any person. Often appears in negative sentences to mean 'to no one'.
この秘密は誰にも言わないでください。
Please don't tell this secret to anyone.
彼は誰にも優しく接する。
He treats everyone kindly.
expression
by anyone; by everyone
Used in passive or potential constructions to indicate the agent is any person. Often in negative form to mean 'by no one'.
この問題は誰にも解けなかった。
This problem couldn't be solved by anyone.
彼の才能は誰にも認められている。
His talent is recognized by everyone.
expression
in anyone; in everyone
Used with verbs or adjectives describing existence, perception, or qualities that reside in people. Often in negative sentences to mean 'in no one'.
誰にも欠点はある。
Everyone has flaws (lit. In everyone there are flaws).
そんな考えは誰にも浮かばないだろう。
Such an idea wouldn't occur to anyone (lit. wouldn't come to anyone's mind).