El actor con el papel secundario hace de protagonista.

In Spanish, hacer de + role/person is a very common way to say to play the part of or to act as.

So:

• hace de protagonista = plays the lead / plays the protagonist

It does not literally mean that he makes something here, even though hacer often means to do or to make in other contexts.

Other possible ways to express a similar idea are:

• interpreta al protagonista
• hace el papel de protagonista

But hacer de is very natural and common.

Because after hacer de, Spanish often uses the role name without an article when you mean serving in that role.

So:

• hace de protagonista = he plays the role of protagonist
• hace de médico = he acts as a doctor
• hace de padre = he plays the father

If you say del protagonista, that would sound more like you are referring to a specific protagonist already identified. In many contexts, that is less natural here.

So the bare noun protagonista is the normal choice when talking about the function or role.

Yes, con literally means with, but here it helps describe the actor:

• el actor con el papel secundario = the actor with the supporting role

This structure is similar to English:

• the man with the hat
• the woman with the red bag
• the actor with the supporting role

So con is introducing a characteristic or identifying detail of the actor.

In more natural English, you might often say the actor in the supporting role or the actor who has the supporting role, but Spanish is happy with con here.

Because in Spanish, adjectives usually come after the noun.

So:

• papel secundario
• coche rojo
• casa grande

Putting the adjective after the noun is the normal pattern.

Sometimes Spanish adjectives can go before the noun, but that usually adds a special stylistic or emotional nuance. Here, papel secundario is the straightforward, standard order.

Here, papel means role or part in a play, film, or performance.

So:

• papel secundario = supporting role
• papel protagonista = leading role
• tener un papel = to have a role

Even though papel also means paper in other contexts, in theatre and film vocabulary it often means role.

A learner may also see:

• rol = role
• personaje = character

But papel is extremely common for acting contexts.

Because Spanish normally uses the definite article with nouns much more regularly than English does.

Here we have:

• El actor = the actor
• el papel secundario = the supporting role

Both nouns are specific in the sentence, so both take el.

English sometimes drops articles in similar expressions, but Spanish usually keeps them.

Because the subject is singular:

• El actor con el papel secundario

The main noun of the subject is actor, which is singular, so the verb must also be singular:

• El actor ... hace

Even though the subject contains extra information (con el papel secundario), that extra phrase does not change the agreement.

If the subject were plural, the verb would change too:

• Los actores con los papeles secundarios hacen de protagonistas

Protagonista is one of those Spanish nouns that can be used for either a man or a woman. The form often stays the same.

So you can say:

• el protagonista = the male lead
• la protagonista = the female lead

In your sentence, protagonista appears without an article after de, so the word itself does not change:

• El actor ... hace de protagonista
• La actriz ... hace de protagonista

The surrounding words show the gender:

• el actor
• la actriz

Yes, but it is not exactly the same structure.

• el actor con el papel secundario focuses on the actor who has the supporting role
• el actor secundario usually means the supporting actor

In many contexts, the two ideas overlap, but the wording is slightly different.

Also, in Spanish, actor secundario can refer to the actor as a supporting actor, while papel secundario refers to the role itself as a supporting role.

Yes, papel secundario is perfectly natural and standard.

You may also hear related expressions such as:

• actor secundario = supporting actor
• actriz secundaria = supporting actress
• papel de reparto = supporting role / ensemble role, depending on context
• actor de reparto = supporting actor / member of the cast

But papel secundario is a very normal and clear choice.

Not in the same way.

• es protagonista means he is the protagonist
• hace de protagonista means he plays the protagonist

The first identifies what he is in the story or production. The second describes the role he performs.

In acting contexts, hacer de is often better when you want to emphasise performance.

Because with interpretar, Spanish usually marks a specific human role with a:

• interpreta al protagonista

So if you use interpretar, the more natural sentence would be:

• El actor con el papel secundario interpreta al protagonista

By contrast, hacer de does not need that structure:

• hace de protagonista

That is one reason learners often find hacer de easier in these role expressions.