Sid Meier's Civilization franchise has been marked by several consistent civilizations and world leaders over the years.
For instance, Elizabeth I and the English have been around from day one, as have Alexander and the Greeks and a few other combinations. But every now and then, a new civilization is injected into the series, as we saw with Brazil in Civ 5 (or rather, the "Brave New World" extension). It was the first appearance for the South American nation, and a surprising one given that we don't think of Brazil as a particularly old country (Portugal, which had a lot to do with settling Brazil, had been included previously).
And now, according to the most recent press release from Fireaxis regarding the upcoming Civilization VI, Brazil is making a return with Pedro II in charge once again.
Dom Pedro II, nicknamed "the Magnanimous", was the second and last ruler of the Empire of Brazil, reigning for over 58 years. Source: https://en.wikipedia.org/wiki/Pedro_II_of_Brazil
This seems to solidify the country as a mainstay in the series, and it looks as if Brazil is even more fleshed out than in the previous game.
For one thing, the animation is completely different. In Civ 5, Pedro II was depicted as an old man, and looked more like a villain from Zorro than anything else, wearing a dark 19th-century suit and seated at an ornate desk. In the new game, he actually more closely resembles an interpretation of a European conquistador depicted in a game called Cashtro's Voyage. That game is one of several casino games based on history and pop culture at Gala Bingo. It actually includes a little introductory video that shows Cashtro as a distinguished figure at loose in a wild world. That's closer to the new image of Pedro II, who remains in uniform but looks younger and is set against the dramatic backdrop of Rio de Janeiro and the surrounding nature.
Also of note is that the specific features of the Brazilian nation appear to have changed quite a bit. If you don't recall Brave New World (or never played it), its Wikia page lists the details, including the unique unit "Pracinha" (which replaced Infantry), and the unique improvement of "Brazilwood Camps." These have both been replaced in Civ 6, with the unique unit now set to be the Minas Geraes, a special battleship that helped Brazil to become a naval power in the early 20th century. The unique improvement, insofar as we can tell at this point, is that you can now build special districts adjacent to rainforest squares in the game. You can also hold a street carnival, and you'll be able to enjoy the interesting feature that Brazil will generate "great people" at an accelerated rate.
Finally, we should also mention that Brazil still looks more like a modern civilization, particularly by comparison to the others that will be included. That is to say, they're not inventing an ancient Brazilian society here, nor are they starting one off with Portuguese explorers to transition into a Brazilian empire. The ruler, buildings, and units for this civilization are all more closely tied to modern history than the ancient world. But one fun result is that there appears to be some focus on athletic stadiums in the Brazilian civilization. Given that, in the real-world, Brazil just created an incredible collection of stadiums for the 2014 World Cup (and did a little bit more for the 2016 Olympics), this is a nice touch from Fireaxis.
Devoted fans of the franchise may feel like this is an unnecessary addition, but the Brazilian Empire seems to have been refined this time around. It looks like a nice piece of Civilization VI, which altogether is shaping up to be a phenomenal game.