Seen as a petty man who enjoyed what little power he wielded, the Fat Man tried to impress people with his so-called "Important Person" routine, where he boasted of how he was once used to protect Jabba's anonymity by being sent out to meet with people. This in turn caused some on Tatooine to believe he was actually the crime lord himself.
Mara Jade, who was posing as Arica to infiltrate Jabba's Palace, saw this as a backhanded compliment; though he was trusted enough to finalize the Hutt's deals, he was effectively "assassin bait," and therefore expendable.
Though no explicit connection exists in canon, the Fat Man is almost certainly one and the same as Heater. The Fat Man's depiction in Sleight of Hand: The Tale of Mara Jade implies that he was intended as a retcon of Declan Mulholland's portrayal of Jabba that was cut from A New Hope, before the scene was later reinserted with a CG Jabba in the Special Edition. Conceived for this same purpose, Heater first appeared in the Star Wars radio drama, taking Jabba's place in a now non-canon version of the scene. Heater's description and backstory in The Essential Guide to Characters, published in November 1995, are nearly identical to the Fat Man's, published just two months later in Tales from Jabba's Palace. It is extremely unlikely that this is coincidental, as Andy Mangels, writer of the Essential Guide, has said that he coordinated information with manuscripts and novels that were in the works. The fact that Melina Carniss—also conceived by Zahn for Mara Jade's short story—first appeared in the guide further suggests this coordination.
Despite this, it is also possible that the Fat Man is Opun Mcgrrrr from the short story Spare Parts (November 1996), whose likeness, too, was taken from Mulholland. Mcgrrr's backstory does not match the Fat Man and Heater's identical one, but as the Fat Man's true name is left ambiguous, he cannot be ruled out. With Heater's only prominent appearance effectively non-canon, it should be noted that Mcgrrr's status in continuity is more stable.
There is also no direct contradiction that would prevent all three of these men, sharing the same physical appearance, from being various personae of one being.
The Fat Man's possible appearance.
Though no explicit connection exists in canon, the Fat Man is almost certainly one and the same as Heater. The Fat Man's depiction in Sleight of Hand: The Tale of Mara Jade implies that he was intended as a retcon of Declan Mulholland's portrayal of Jabba that was cut from A New Hope, before the scene was later reinserted with a CG Jabba in the Special Edition. Conceived for this same purpose, Heater first appeared in the Star Wars radio drama, taking Jabba's place in a now non-canon version of the scene. Heater's description and backstory in The Essential Guide to Characters, published in November 1995, are nearly identical to the Fat Man's, published just two months later in Tales from Jabba's Palace. It is extremely unlikely that this is coincidental, as Andy Mangels, writer of the Essential Guide, has said that he coordinated information with manuscripts and novels that were in the works. The fact that Melina Carniss—also conceived by Zahn for Mara Jade's short story—first appeared in the guide further suggests this coordination.
Despite this, it is also possible that the Fat Man is Opun Mcgrrrr from the short story Spare Parts (November 1996), whose likeness, too, was taken from Mulholland. Mcgrrr's backstory does not match the Fat Man and Heater's identical one, but as the Fat Man's true name is left ambiguous, he cannot be ruled out. With Heater's only prominent appearance effectively non-canon, it should be noted that Mcgrrr's status in continuity is more stable.
There is also no direct contradiction that would prevent all three of these men, sharing the same physical appearance, from being various personae of one being.