Learn Spanish (Latin America): Fue el asistente quien desenchufó la fotocopiadora. - It was the assistant who unplugged the photocopier.

Starting with Fue creates a cleft sentence to add emphasis. By saying Fue el asistente quien... (It was the assistant who...), you are putting a strong spotlight on the assistant, likely to clear up confusion or assign blame, rather than just stating a simple fact.

Does the verb Fue match el asistente, or is it always third-person singular in this structure?

The verb ser must match the person or thing you are emphasizing. Here, el asistente is third-person singular, so we use fue. If you wanted to say 'It was me who unplugged it,' you would change it to Fui yo quien..., matching the verb to yo.

Could I use que or el que instead of quien in this sentence?

Yes. When emphasizing a person in a cleft sentence, you can use quien, que, or el que / la que. Saying Fue el asistente el que desenchufó... would also be perfectly natural and correct. Using quien often sounds just a little more formal or precise.

What is the root of the verb desenchufó?