So, I'll start with his anime appearance, because there's a lot less going on here.
Long story short, Lupin and the gang are roped into a death game, where people on the Internet bet on which of the professional assassins competing will be the first to kill Lupin. King is one of the contestants there... and, that's about it.
What makes his appearance in Part 5 more interesting to me, however, is King's use in the manga. Like... the untapped potential for

angst

and

drama

in the Part 5 anime episode haunts me, y'all. Let me explain...
The Lupin Empire is NOT in Good Health, actually. Lupin gets himself injured in a train wreck. (And, I swear to God, I did NOT choose this chapter due to recent personal events, lol, I just wanted to talk about King and forgot the chapter begins like this.)
Okay, so, Lupin is in the hospital, and, some dude just, like, waltzes right in and tries to shoot him point blank right in front of the doctor and nurse like an absolute madman. UM??? SIR??? Unhinged behavior. But, like Han Solo, Lupin shot first in spite of his wounds. Some time later, he wakes up in Fujiko's house, who informs him that his father, Lupin II, is dead, and that everyone in the Lupin Empire is out to get him... even her. And, as she adds... even Jigen.
Ah, early Lupin manga, you and your cheeky little quirks... it's interesting to look back on concepts MP was experimenting with. Lupin specifies that Jigen is an old friend, though Lupin does mention how he and Jigen "didn't always get along". However, Jigen is now working under King, the new head of the Lupin Empire. Granted, much like how modern Jigen would never even think to double-cross Lupin, Jigen is only serving King because...
... and, get this horseshit...
... King is holding his
sister hostage.
EXCUSE THE FUCK ME,
WHOMST???
JIGEN HAD A SISTER??? APPARENTLY???
To those of you who live in the alternate universe where MP decided to explore this concept further, please tell me what it's like living in the best timeline.
In all seriousness, we do see shreds of Jigen's devotion to Lupin, where, even though he is forced to help someone else, he still apologizes to Lupin for the shitty circumstances and even defends Lupin when both Fujiko and King underestimate Lupin's skills... I feel this sort of works as a
better Goodbye Partner proto-Goodbye Partner. Jigen is, for the most part, a passive character. Shit happens to him, and he's just like, "welp, I guess this is my life now

" --- King is a pompous jerkass, but Jigen still back-talks and sasses him when he gets the chance. King throws a little bitch fit whenever Jigen reminds him of how pissed Lupin will be once he discovers King is the one responsible for killing Lupin II, but Jigen does not retaliate whenever King shatters a vase on his head. To me, it shows he's just, in Lupin's oh-so-eloquent Tokyopop translation words, "be[ing] bitch to the top dog" order to protect his sister--- yet his true loyalties lie with Lupin in the end. Though, we do never get closure on whether or not Jigen's sister is alive in the end, which is unfortunate. I guess she exists in the same shadow realm MP banished Jigen's brother to.
King is an asshole, plain and simple. He's the one responsible for the train wreck, which resulted in the deaths of 53 people, including Lupin II. He usurps the title of the leader of the Lupin Empire for himself. He and orders his unnamed henchman and Jigen to kill Lupin in order to tie off the loose ends. Speaking of Jigen, King holds his sister hostage in order to secure his cooperation. He also wins over Fujiko to his side, and ends up sleeping with her. THIS GUY KILLED LUPIN'S DAD
AND HE STOLE LUPIN'S WOMAN, HIS MAN, AND HIS WHOLE ASS CRIMINAL EMPIRE... YET, HE APPEARS AS A SINGLE ONE-OFF CAMEO IN THE ANIME??? Someone please explain this to me, the math is not mathing. This man won. He literally won. He's accomplished more than what most other villains in this series could ever hope for, and managed to steal everything of worth to Lupin.
Hell, Jigen is even on the verge of executing Lupin once Fujiko lures him over and subdues him, but... Lupin snuck a bomb under Fujiko's shoe, and both she and King explode in the middle of their premature copulatio--- er, I mean, celebration.
I need a melodramatic re-write of Episode 3 where King is depicted as the true menace he is. I need this so bad.