a su tío

his/her uncle

→ a
phrase Rare #23,363
his/her uncle The a is the personal a used before a person who is a direct object. Su can mean his, her, or your in the formal usted form, depending on context.
SP: Acompañó a su tío al médico.
EN: He accompanied his uncle to the doctor.

Él llamó a su tío tan pronto como llegó a Matsuyama.

He called his uncle as soon as he arrived in Matsuyama.

Él visitará a su tío.

He will visit his uncle.

Él envió una carta dirigida a su tío.

He sent a letter addressed to his uncle.

Tom le escribe a su tío.

Tom writes to his uncle.

Ponemos a su tío Pánfilo de juez.

We appoint their uncle Pánfilo as judge.

— Algunos hombres buenos (1992)

Visitó a su tío ayer.

He visited his uncle yesterday.

Helen visita a su tío cada domingo.

Helen visits her uncle every Sunday.

Ella visitó a su tío y a su tía.

She visited her uncle and aunt.

Tiene que parecerse al padre, no a su tío.

He has to look like his father, not his uncle.

— Burning (2018)

Él dirigió la carta a su tío.

He addressed the letter to his uncle.

Lo llamaron Horatio como a su tío.

They named him Horatio, after his uncle.