The Star Wars franchise has introduced viewers to a wide range of aliens, many of which are iconic. Some of these have become easy to recognize because of characters with notable roles. Any fan can recognize a Wookiee or a Hutt because they are familiar with Chewbacca and Jabba. One rare enigmatic species is easy to identify because it included Yoda and Grogu. And unfortunately, Gungans are rather infamous because of Jar Jar Binks. But overall, the films have mainly emphasized human characters, with aliens sometimes filling out supporting roles.
Some races do not even get that. Several iconic species were only used for background characters. For example, the Mos Eisley Cantina scene of A New Hope introduced a ton of now-popular alien species that only acted as extras. The Book of Boba Fett has worked hard to change this pattern. Although its main characters are still human, it has made a point of bringing in a lot more diversity in its cast - with several background races now having opportunities to take center stage.
5 Gamorreans
Gamorreans first appeared in Return of the Jedi where they acted as bodyguards to Jabba the Hutt. From the start, it was obvious they were meant to come off as gross and unpleasant. The pig-like appearance was probably meant to reflect the level of decadence going on in the palace. They were present both in Jabba's Palace and his sail barge but spent most of their time in the background. The biggest role any of them had was the one who accidentally got dropped into the rancor pit with Luke, who was then eaten by the creature to his boss's enjoyment. This gave them a reputation for being dim-witted brutes and hired thugs, making them popular as henchmen for the expanded universe.
The Book of Boba Fett not only brings Gamorreans to the forefront but brings two of the gamorreans from Return of the Jedi into its main cast. In an interesting turn of events, Boba Fett is presented with two Gamorreans who used to work for Jabba and offers them an opportunity to work for him instead. They accompany him throughout the series, often supporting Boba in difficult situations and showing an impressive amount of loyalty.
4 Ithorians
The Ithorians are a very distinctive race - they can easily be spotted by their oddly-shaped head. This species has been around since the beginning, first appearing in the cantina scene of A New Hope, but in the films, they mainly acted as extras for crowd scenes. In the Expanded Universe, it was revealed that they have some strange biological quirks, such as two mouths. They also have a culture based on revering nature that values pacifism, giving them a reputation for favoring diplomacy over violence. But a lot of the time they have been cast in supporting roles at most.
The Book of Boba Fett rectifies this with the introduction of Mok Shaiz, the Ithorian mayor of Mos Espa. Shaiz has made regular appearances throughout the series, acting as a major antagonist. From refusing to pay tribute to possibly sending assassins after Boba Fett, he has caused a lot of problems. But he was also responsible for a major plot point by making a deal with the Pike Syndicate, one which effectively sold out Boba Fett and threatened everything he has been working towards.
3 Trandoshans
The reptilian Trandoshan race was first introduced in The Empire Strikes Back through its most iconic member - the notorious bounty hunter Bossk. Though perhaps not on the same level as Boba Fett, Bossk's appearance quickly resonated with viewers and he developed his own following. Pretty impressive for a character who only appeared in one scene and had a single line of dialogue - spoken in an alien language with no subtitles - plus a cameo in Return of the Jedi. Bossk was among the bounty hunters recruited by Vader to track down Han Solo, something he was beaten to by Boba Fett.
Trandoshan culture would later be explored in the Expanded Universe, where it was shown their society was built on hunting and collecting trophies, a bit like the Predator. They even worshipped a goddess whose favor was earned by delivering pelts from challenging kills. The emphasis on hunting in their culture drives many of the species to seek out potential targets, often looking for bigger and better ones to collect trophies from, and sometimes that included hunting sentient beings.
Unsurprisingly, that does put them at odds with other races- especially Wookiees, who they see as ideal prey. Because of this reputation, the majority of Trandoshans are portrayed as antagonists - either as hunters or members of the criminal underworld - or both. The Book of Boba Fett emphasizes the latter, although the ones seen here are not his enemies - at least not currently.
2 Tusken Raiders
The Tusken Raiders, more commonly referred to as the "sandpeople" made a pretty large impact on fans and became well-recognized as one of the most common dangers one can face on Tattooine. But it is easy to forget they actually had a pretty small role in the movies. They were only on-screen for a few minutes of A New Hope before Obi-Wan manages to scare them off. And yet they became such a distinct species - their strange outfits, hidden faces, and an instantly recognizable battle cry. If anything, they may have overshadowed a lot of much bigger and more dangerous threats on the planet, like Krayt Dragons.
To be fair, Sandpeople have been shown on various occasions since then, with some attempts at humanizing them, from Knights of the Old Republic to The Mandalorian, but The Book of Boba Fett gives them a storyline of their own. In fact, they are a key part of Boba Fett's development.
Though initially imprisoned and enslaved, Boba Fett is able to earn their respect enough to the point where he is recognized as a member of the tribe. He tries to help them deal with problematic neighbors and is deeply hurt when they are massacred. This is a huge leap from A New Hope, where they were mainly present to emphasize the potential dangers of Tattooine.
1 Twi'leks
Every Star Wars fan knows the iconic Twi'lek race, but in the actual films, they were never given much of a role. They first appeared in Return of the Jedi and made their way into the backgrounds of some later films. Arguably the most prominent Twi'lek in any of the films is Bib Fortuna, a supporting antagonist in the first act of Return of the Jedi who later made a cameo in The Phantom Menace.
Beyond him the two best-known were Oola, the slave Jabba fed to his rancor; and Aayla Secura, a Jedi seen in the background of Attack of the Clones and gets one scene in Revenge of the Sith where she dies. Neither has a single line of dialogue. Viewers not versed in Star Wars lore could be forgiven for not immediately realizing that senator Orn Free Taa was also a member of the species, due to him looking different from the image they are probably used to.
The Expanded Universe worked to rectify this. Both timelines have had stories of strong and capable Twi'leks like Mission Vao in Knights of the Old Republic. There were entire storylines of The Clone Wars, Rebels, and The Bad Batch centered around their homeworld of Ryloth, not to mention the introduction of fan-favorite Hera Syndulla in Rebels.
However, The Book of Boba Fett brings them into live-action with not one but two members of the species having notable roles. The currently-unnamed assistant of Mayor Mok Shaiz has been a notably recurring role; but more interesting is Garsa Fwip, owner of the Sanctuary bar that has been visited throughout the series.