a

If the direct object of an active verb is a definite person (or personified animal or thing, as in a fable, for instance), the preposition a, untranslated in English, is inserted before it.

Busco mi sombrero. - I look for my hat.

Busco a mi hija. - I look for my daughter.

Busca a Carlos. - I look for Carlos.

The first object is a thing. The second and third are people.