Here's what the main players in The Mandalorian were up to during Star Wars' original trilogy. Set in 9 ABY, The Mandalorian occupies a neat little section of Star Wars timeline. Five years have passed since Return of the Jedi, so the Disney+ series isn't dealing with the immediate aftermath of the Empire's collapse, but the Star Wars sequel trilogy remains 20 years out - no need to start worrying about the First Order or flying Stormtroopers quite yet. Because The Mandalorian sits so close to the original trio of movies, however, virtually every character introduced by the Disney+ series was alive between A New Hope and Return of the Jedi.
Indeed, character has been one of The Mandalorian's greatest strengths. Din Djarin is a fascinating protagonist, despite rarely showing his face, and Grogu is a worldwide icon, despite not yet uttering a single (coherent) word. Elsewhere, the likes of Greef Karga and Fennec Shand have become fascinating supporting figures in the Star Wars tapestry, and familiar names such as Boba Fett and Bo-Katan Kryze are greatly expanded upon.
Of course, the inevitable drawback of bringing fresh blood into Star Wars is having to explain why fans haven't seen them before. In some cases this is obvious, and in others a backstory is provided, duly accounting for a protagonist's whereabouts five years ago. For some, the past is more ambiguous, leaving viewers to assemble the clues for themselves. This is where The Mandalorian's villains and vigilantes were while Luke, Han and Leia were kicking the Empire out of town.
Din Djarin
Din Djarin's Star Wars backstory largely hinges upon when the mysterious Great Purge of Mandalore takes place. The Mandalorian reveals Djarin became orphaned during the prequel trilogy era, and was taken in by Mandalore's warriors as a foundling. Indoctrinated and trained by the Children of the Watch, Djarin was based on Mandalore, faithfully honoring "the Way" alongside the rest of his people. This period of relative calm might have overlapped with the Star Wars original trilogy, but at some point between 1 BBY and 4 ABY, the Empire launched a full-scale attack on the Mandalorians - a civilization Palpatine's goons had thus far failed to conquer. The resulting Great Purge pushed Din Djarin and the Children of the Watch into hiding on planets such as Nevarro, where they operated in secret. This tribe includes Djarin, The Armorer, and Paz Vizsla.
While Star Wars' original trilogy rumbled on, Din Djarin would've been working as a bounty hunter, still living in the shadows among his fellow zealots. With that said, Din might've still been living on his adopted home planet of Mandalore during A New Hope. More will be revealed as The Mandalorian dives deeper into the Great Purge.
Grogu
Grogu's history remains one of The Mandalorian's biggest mysteries, but the youngster almost certainly endured a tough time during the Star Wars original trilogy. Thanks to Ahsoka Tano, it's known that Grogu trained at the Jedi temple during the prequel movies, and was rescued from Order 66 by an unknown figure. This enigmatic savior placed Grogu into hiding on Arvala-7, and seemingly hired guards to protect the facility. In all likelihood, Grogu spent the entire original trilogy locked away in secret, somehow given a source of sustenance (probably not as tasty as blue cookies and frog eggs). Since there's no indication when Grogu first arrived on Arvala-7, he potentially experienced other misadventures during the first three Star Wars episodes. The Mandalorian season 3 can explain Grogu's past more fully.
Greef Karga
Carl Weathers' head of the Nevarro Bounty Hunters' Guild begins as a morally ambiguous entity in The Mandalorian, before finally landing on the side of heroism. Karga has evidently been involved in the Bounty Hunters' Guild for some time, and since the organization existed both before and during the Imperial era, it's likely his role remained unchanged from the original trilogy into The Mandalorian, still arranging missions and paying bounties. Greef Karga's aborted plan to abduct Grogu proves his willingness to work with the Empire when necessary (even after their downfall), so it's perhaps natural to assume he cooperated with Imperials during the original trilogy too. Greef's actions in The Mandalorian might be the conscience of a guilty man seeking redemption.
Cara Dune
Before The Mandalorian, Cara Dune served as a shock trooper for the Rebel Alliance - a career she was inspired to pursue following the destruction of her home. Dune hails from Alderaan, but was fortunate enough to be elsewhere when the Death Star chose her planet for target practice. Only after the events of A New Hope did Dune join the Rebellion, and it's suggested she played a part in Return of the Jedi's Battle of Endor. Cara claims to have been active mostly after the Empire's fall, implying she played little role in the famed skirmishes of Star Wars' first three movies. Logically, Cara Dune would've spent most of the original trilogy in Rebel training, before getting involved off-screen toward the end. Since Lucasfilm won't be working with Gina Carano again, Cara Dune's past probably won't be developed further.
Fennec Shand
Hunted by Din Djarin and a young upstart by the name of Toro Calican, Ming-Na Wen's Fennec Shand is already a respected and experienced bounty hunter during her The Mandalorian debut on Tatooine. Star Wars: The Bad Batch, however, proves Shand was an upstart herself shortly after the Empire came to power. Though hunting down The Bad Batch's Omega clearly isn't her first rodeo, it's clear that Shand's fearsome reputation grew thanks to her exploits during the original Star Wars trilogy, and most likely involved a healthy working relationship with the Empire. This tallies with the character hiding in The Mandalorian - The New Republic put a bounty on Shand's head, strongly hinting her services were popular with the bad guys.
Moff Gideon
While there are still holes to be filled in Moff Gideon's backstory, The Mandalorian's main villain was undoubtedly a busy boy during the original Star Wars trilogy. As confirmed by Cara Dune, Gideon served in the Empire's ISB (Imperial Security Bureau) at the time of the Great Purge, meaning he probably held that same position for much of the original trilogy era. As Palpatine's very own Gestapo or KGB, the ISB was a ruthless division charged with uncovering and quashing resistance to the current regime. During his time with the ISB, Gideon may have been involved in hunting insurgents such as the Spectres from Star Wars Rebels, Nightswann and, eventually, the likes of Mon Mothma and Leia Organa as the Rebellion gained prominence, possibly working with the likes of Grand Admiral Thrawn whilst doing so.
Nevertheless, evidence suggests Moff Gideon always held a special interest in Mandalorians. Rogue One (set shortly before A New Hope) includes a reference to "Project Black Saber" - a potential hint toward the Empire's plans for Mandalore. Given Gideon's preoccupation with the planet and its heritage, he must've spent at least some of the original Star Wars trilogy plotting what would later become the Great Purge.
Migs Mayfeld
Bill Burr's Migs Mayfeld first appears in The Mandalorian as a morally-questionable mercenary, he served as an even more morally-questionable Imperial sharpshooter during the original trilogy era of Star Wars. Mayfeld's past is confirmed when Burr returns in The Mandalorian season 2 and references Operation: Cinder, as well as the tragedy of Burnin Konn. Op Cinder was Palpatine's contingency in the event of his own death - a brutal assault to wipe out various planets that once fell under his jurisdiction. In the process of carrying out the operation on Burnin Konn, Valin Hess ordered a city destroyed, killing thousands of Imperial troops already on the battlefield. Mayfeld was one of very few survivors It's not specified exactly how long Migs served the Empire, but at least some of his OT years were spent sniping folk for Palpatine.
Boba Fett
Boba Fett is one of precious few characters in The Mandalorian whose whereabouts are entirely accounted for during the classic period of Star Wars. The bounty hunter pops up alongside various others as part of a motley crew Darth Vader hires to locate the Millennium Falcon in The Empire Strikes Back. More than happy cosying up alongside the Empire, Boba Fett locates Han Solo at Cloud City and encases him in carbonite, hauling the life-sized collector's edition model to Tatooine for Jabba the Hutt's bounty. Fett would make the mistake of lingering at Jabba's palace, and became caught up in Luke Skywalker's rescue mission, getting tossed into the Sarlacc pitt for his troubles.
Wider Star Wars media has elaborated on Boba's story, chronicling his movements during A New Hope. The bounty hunter apparently began searching for the Empire's two most wanted droids, R2-D2 and C-3PO, before his attentions were drawn to Han Solo instead. Boba worked with Darth Vader on various missions prior to their dalliance in The Empire Strikes Back, and even confronted Luke Skywalker on the Dark Lord's orders.
Bo-Katan Kryze
In complete contrast to Boba Fett, next to nothing is known about Bo-Katan Kryze's life while the Empire and Rebellion were knocking chunks out of each other across the galaxy. The animated Mandalorian princess is seen accepting the Darksaber and becoming her planet's rightful ruler in 1 BBY, and next appears played by Katee Sackhoff in The Mandalorian season 2, embittered and determined, but offering no information on how she spent the past decade. Bo-Katan's untold story is all tied up in the aforementioned Great Purge, and could be revealed in The Mandalorian season 3.
Ahsoka Tano
Like Bo-Katan Kryze, Ahsoka Tano is a major character from the animated Star Wars world conspicuous by their absence during the original trilogy timeline. At the end of Star Wars Rebels, Ahsoka escapes the World Between Worlds and finds herself on Malachor, promising to find Ezra Bridger, who she was separated from inside the mystical plane. This occurs in 0 BBY, on the precipice of A New Hope, but Ahsoka is next seen on Lothal following the Empire's Return of the Jedi defeat, still hunting for Ezra. What she did and where she went between those two points is anyone's guest. Most likely Ahsoka was ducking and dodging the pursuit of the Empire, and The Mandalorian suggests she might've even been tracking down Thrawn off-screen. The truth should become clear in Rosario Dawson's Ahsoka Disney+ series.
Dr. Pershing
There's a fascinating untold backstory in The Mandalorian's Dr. Pershing. So lacking in empathy he could take a scalpel to Baby Yoda, Pershing is Gideon's personal cloning specialist, and is deeply invested in using Grogu's Force-sensitive genes for some sinister intention. Pershing also has connections to Kamino, which raises questions over his placement during the Star Wars original trilogy. Either Pershing was already a student of Kamino's fabled cloning operation, but opted to side with the Empire in order to fulfill his dark scientific ambitions, or he was purposely sent by the Empire to Kamino to learn their methods. Pershing seems to have always been affiliated with Moff Gideon (which might explain why he's absent in the OT), but it's not clear whether he was recruited during Imperial reign, or whether Gideon headhunted the specialist after forming his offshoot cell following the Battle of Endor.