*In charge of* is a complex preposition like *in place of*, *in spite of*, *in view of*, or *in case of*. It means having responsibility for or jurisdiction over someone or something. *In the charge of* is a preposition phrase meaning in the care or custody of someone.

A similar change in meaning occurs when the definite article is inserted into the complex preposition *in view of*. *In view of* means *because of* and *in the view of* means *in the opinion of*.