era o único

was the only one

→ ser
phrase Uncommon #18,900
was the only one Used to say that someone or something was the only one in a particular situation. The adjective "único" agrees in gender and number with the noun it describes; in this exact phrase, it is masculine singular.
PO: Tom era o único que poderia fazer isso.
EN: Tom was the only one who could do that.

Tom era o único garoto da turma.

Tom was the only boy in the class.

Tom era o único estudando quando eu entrei na sala de aula.

Tom was the only one studying when I entered the classroom.

Tom não era o único a chorar.

Tom wasn't the only one crying.

Eu olhei ao redor e percebi que era o único carro na estrada.

I looked around and realized I was the only car on the road.

Esse não era o único problema.

That wasn't the only problem.

Você era o único amigo dele.

You were his only friend.

Tom era o único filho de Maria.

Tom was Maria's only son.

Tom não era o único a comer.

Tom wasn't the only one eating.

Tom era o único amigo de Mary.

Tom was Mary's only friend.

Você era o único na sala do servidor.

You were the only one in the server room.

— Invasores - Nenhum Sistema Está à Salvo (2014)

O Tom não era o único lá.

Tom wasn’t the only one there.

Tom era o único garoto da sala que Mary gostava.

Tom was the only boy in the class that Mary liked.

Tom não era o único acordado.

Tom wasn’t the only one awake.

Eu era o único lá que não sabia que o Tom queria fazer aquilo.

I was the only one there who didn’t know Tom wanted to do that.

Eu não percebi que aquele era o único dia.

I didn't realize that was the only day.

— Campo dos Sonhos (1989)

Tom era o único canadense na sala.

Tom was the only Canadian in the room.