Learn Dutch: De onderhandelaar smeekt de dader om ermee te stoppen. - The negotiator begs the perpetrator to stop it.

This sentence uses a structure called "object control." With verbs of ordering, advising, or begging like smeken, the object of the main sentence (de dader) automatically acts as the logical subject of the following infinitive action (stoppen). The negotiator does the begging, but the perpetrator is the one who is expected to do the stopping.

Where does ermee come from in this sentence?

It literally translates to "with it." In Dutch, "to stop doing something" is expressed as stoppen met. However, you cannot combine the preposition met with the normal pronoun het (it). Instead, they merge and change into the pronominal adverb ermee.

Is the word om strictly necessary to introduce the infinitive clause?

No, you could technically leave it out and say "De onderhandelaar smeekt de dader ermee te stoppen". However, with verbs that try to influence someone's behavior, using om before the te-infinitive is highly idiomatic and generally preferred in everyday Dutch to make the sentence flow better and clearly mark the requested action.

What is the origin of the word dader?

De dader translates to "the perpetrator" or "the culprit." It is directly related to the verb doen (to do) and the noun de daad (the deed or act). Therefore, a dader is literally the "doer" of a specific, usually criminal, act.