'The Falcon and the Winter Soldier' delivers on its promise of a major cameo. Here's what the character could mean for the MCU.

• Warning: There are major spoilers ahead for episode five of "The Falcon and the Winter Soldier."
• The episode featured a character named Contessa Valentina Allegra de Fontaine, who goes by Val.
• The mysterious character was played by Emmy-winning "Veep" star Julia Louis-Dreyfus.

After hyping up a major cameo to come on "The Falcon and the Winter Soldier," the penultimate episode of season one delivered on that guarantee.

Episode five, titled "Truth," was expected to be a major episode of the Marvel series.

"TFATWS" head writer Malcolm Spellman previously told ComicBook.com that he was most excited for fans to see episode five because "it just gets real" and will make people cry.

And in an interview with Rotten Tomatoes, Spellman teased a cameo on episode five.

"There are characters in our series who I would love to see partnered with like - it's a very, very grounded character - partnered with one of the big world-shakers like Thor or someone like that," he said. "The personality is so strong, it's the episode five character. I'd love to see that character with Thor."

More recently, Slash Film reported that "this surprise character is not one that we've seen in the MCU before and not one who is primed to appear in an upcoming film."

"However, we have learned it is an existing Marvel Comics character who is played by a well-known performer," The publication reported.

The much-anticipated cameo took place almost 15 minutes into the episode, after John Walker was stripped of his title of Captain America due to his very public murder of a Flag Smasher during the prior episode.

As John's wife, Olivia Walker, was talking him through his next course of action, they were interrupted by a woman walking toward them. After taking off her sunglasses, the person was revealed to be 11-time Emmy-winning "Veep" star Julia Louis-Dreyfus.

Dreyfus' character introduced herself to the couple as Contessa Valentina Allegra de Fontaine, also known as Val.

Val told John that she would have killed the Flag Smasher too and, ignoring Olivia's question about who she is, revealed that she knows John took the super-soldier serum.

"It has made you very, very valuable to certain people," she said. "I actually think it was the second-best choice you've ever made in your life."

She said that there were two actions tied for the first place: marrying "fabulous firecracker" Olivia and "picking up the phone when I call you."

Val also revealed that she knows John no longer has the shield (which Sam and Bucky took during an earlier confrontation) and planted the seed for John to make his own version by reminding him that the prized possession "doesn't really belong to the government."

Then she left a seemingly blank business card and said, "I'll be in touch."

The appearance of Louis-Dreyfus left viewers with plenty of questions about who she's playing and what the character's motive is.

Interestingly, Vanity Fair reported that Louis-Dreyfus was supposed to make her Marvel debut in "Black Widow," which was originally supposed to be released in 2020 as the first project as part of phase four. "Black Widow" was supposed to be followed by "TFATWS," then "WandaVision."

But due to the pandemic, the order of the three projects was reversed, and "Black Widow" is now slated to hit theaters and Disney Plus on July 9. Vanity Fair also reported that Louis-Dreyfus seemingly teased her involvement in the MCU two years ago in an interview with the publication.

Following Louis-Dreyfus' cameo on "TFATWS," people theorized that the actress is portraying the elusive Power Broker, who's a key figure on the show but has yet to be seen. Val's interest in John taking the serum suggests that she could be the Power Broker, who's known as the judge, jury, and executioner in Madripoor.

Episode three of "TFATWS" also revealed that the Power Broker funded Dr. Nagel's recreation of the super-soldier serum. Because Karli Morgenthau stole the serum, she and the Flag Smashers are enemies of the Power Broker.

Other fans have also suggested that perhaps Sharon Carter is the Power Broker. She's been on the run since betraying the government in "Captain America: Civil War" and has been hiding out in Madripoor, where she's well-connected and has been paying the villain Batroc for jobs.

Others theories about Val's identity could be found in the comics.

In the source material, Val was a triple agent with Russian origins who worked with S.H.I.E.L.D., Hydra, and Leviathan. She also had romantic storylines with S.H.I.E.L.D. director Nick Fury and Steve Rogers/Captain America. In addition, Val worked with Sharon Carter as part of an all-female group known as the Femme Force.

Among Val's many adventures in the comics was one involving her being captured and replaced by a Skrull imposter. She also became Madame Hydra and was heavily involved in espionage, while still remaining loyal to the organization Leviathan.

Spellman also previously told Entertainment Weekly that "TFATWS" ties into at least three Marvel projects.

With "Black Widow" and shows like "Secret Invasion" (which will star Samuel L. Jackson as Nick Fury and center on Skrulls) on the horizon, there are plenty of possible theories on how Louis-Dreyfus' character fits into the MCU.

It's unclear how closely the MCU will follow the comics or how much they'll adapt from the source material, so fans will have to wait until next week's season finale for more answers about who Val is.