If there’s a character that can be singled out to be the fanbase’s darling in Supernatural, it would have to be Jack Kline. Introduced as the son of Lucifer, Jack went against his supposed fate as the next evil being to become a genuinely lovable character with few flaws.
However, with his innately pure nature arose a number of gaps in personality, as Jack just wasn’t developed enough to understand how to separate certain things from good to bad. Due to this, it can’t be said that Jack didn’t have any negative traits, as these were on display side-by-side to his positive attributes.
Worst: His Extreme Naivete
There were a few storylines that fans hated where Jack was placed as a tool by the characters for their own nefarious needs. The issue here is the fact that he was so naive that it was too easy to take advantage of him, eventually causing a lot more harm than good.
This is what got Billie to convince him to become a bomb, with Jack not even questioning her as it later turned out she just wanted to kill Chuck to become the strongest being in the universe. The angel Duma did the same, convincing Jack easily to do her dirty work so she could take over Heaven.
Best: His Ability To Inspire Others To Be Good
Due to the mixture of his boyish optimism and adorable nature, Jack had the tendency to bring the best out of those around him. It was after Castiel connected with Jack that he learned to truly be caring to a selfless degree, while Sam also grew into a paternal role.
Jack’s act of turning Heaven into a paradise in the series finale was what gave Dean the peace of knowing that he and Sam would be reunited, which is how the show ended. Overall, Jack inspired others to be good even if he didn't realize it.
Worst: The Reckless Use Of His Powers
It can be argued that Jack used his powers when they were needed, but he ultimately made the wrong decisions with them as well. The biggest instance of this fact was to burn off his soul to kill Alternate Michael, something turned him soulless and completely apathetic.
Jack caused the world to temporarily plunge into chaos when he influenced everyone to tell the truth all the time, something that required the intervention of God to fix. He also nearly killed the teenagers he hung out with, all due to the reckless use of his abilities.
Best: Being Completely Selfless
If there’s one thing certain about Jack, it’s that he’s selfless to the core. He never portrayed any need to be considered important, instead choosing to fight when he was only a couple of years in age. This trait was such that Jack displayed it before he was even born.
It was Jack empowering Castiel from the womb that allowed him to kill Dagon, proving how he was meant to be a good soul that didn’t have any selfish characteristics. He almost got himself killed to end Chuck and Amara, where Jack didn’t display any fears or hesitancy.
Worst: Placing Far Too Much Faith In The Winchesters
Jack considered Sam and Dean to be his parents just as much as Castiel. This turned out to be the wrong way to assess them, as the Winchesters attempted to betray Jack by sealing him in the Ma’lak box and also tried to take his life.
While Jack had it right with Castiel and Sam to an extent, as they did truly care for him, he placed his faith in the wrong hands with Dean who ultimately became something of a villain when he tried to kill Jack and said he was never like family to him.
Best: Never Holding A Grudge
Jack was killed in the Season 14 finale, which was when Dean had come close to killing him. He made his return midway in Season 15, where he never brought up what Dean tried to do. Jack even considered forgiving the atrocities committed by Lucifer, hoping his father had changed.
After regaining his soul, Jack overlooked the Winchesters’ attempts to seal him in the Ma’lak box, while not holding it against Castiel for failing to control him when he was soulless. As far as holding grudges is concerned, Jack didn’t really know how to.
Worst: Always Thinking He's The Problem
By learning he was the son of Lucifer and supposedly an abomination, Jack got it in his head that everything was his fault. He took Dean’s angry words to heart by convincing himself that the troubles they were facing came about due to his birth.
Making things worse is how he didn’t heed the words of Sam and Castiel, who assured Jack numerous times that they didn’t see him as a villain. Unfortunately, he had the habit of focusing on the negative perception about him rather than the positive ones.
Best: His Friendly Nature
This was something he derived from Sam, as Jack remained an approachable person who didn’t think ill of anyone. Despite being at a social disadvantage -- he was a toddler-aged spawn of Satan, after all -- Jack tried his best to fit in.
It was a learning process for him to understand how he could be like a normal person, but his friendly nature was something that had always been intrinsic to him. Although he might not have always been treated the same way in return, no one can accuse Jack of not being sociable himself.
Worst: Wanting To Please Everyone
A big flaw in Jack’s personality was his belief that he had to please everyone to avoid any conflicts. He didn’t realize that it wasn’t his job to do so but forced himself to be a people-pleaser due to his belief that he was the root of the problem.
In his bid to make everyone happy, Jack would traumatize himself when the desired effect didn’t take place. His entire attempt to sacrifice himself in Season 15 was due to Jack’s hope that this would make Sam and Dean happy with the knowledge that he tried to make amends for accidentally killing Mary.
Best: Never Displaying Any Sinister Intentions Despite His Incredible Powers
It was teased before his birth that Jack might be included in the list of villains, but he never got around to it. His soulless state wasn’t malicious either, as he couldn’t control his apathetic mindset. It’s a pretty remarkable trait that he didn’t get swayed by the lust of power considering how powerful he actually was.
Jack was shown to be stronger than any archangel ever made, with the capability to plunge the world into chaos. And yet, he didn’t choose to be the villain that Chuck turned out to be, even giving humans the chance to make their own choices after he became God.