Do-won, much like Blondie, is a gunslinging bounty hunter Anti-Hero who mows down the most people out of all of them. However, he has a stronger moral code and his Greed is much less severe. At least, the only money he's after is the bounty on the Finger Chopper's head.
Chang-yi is much more well-rounded than Angel Eyes and has the extra insecurity of being Always Second Best. He's no less cool in spite of this.
Tae-goo's past is even uglier than Tuco's, if that's possible. Other than that, the two are very similar in their body language and their disarmingly goofy mannerisms. Furthermore, Tae-goo's relationship with Do-won, the respective "Good", is purely platonic, whereas Tuco's hare-brained revenge schemes and manipulation tactics against Blondie are laced with Foe Yay.
Crazy Awesome: This is how Tae-goo has managed to stay alive for so long. In the extended ending, he even survives by wearing a metal plate beneath his quilted shirt.
Draco in Leather Pants: Chang-yi fits the mould of an ideal bad boy. He's dark, he's brooding, sexy and tortured. Which makes people gloss over the fact that he's a neurotic psychopath who brutally murders people.
Tae-goo gets this as well, for being so darn endearing.
In the extended ending, while preparing to blow up Chang-yi's corpse, Tae-goo finds himself surrounded by the Japanese army, so he threatens them with a stick of dynamite and flicks the lighter close to it. The army retreats, and Tae-goo slowly realises that he actually lit the dynamite by mistake. His reaction is priceless.
In the Ghost Market fight, Do-won asks Tae-goo to run to the other side of the street so he can see where they're shooting from.
Tae-goo: Why does it have to be me?
Do-won: Is there anyone else?
(Tae-goo goes to the other side of Do-won and glances round the corner)
Tae-goo: Should I run in a straight line, or go in a zig zag and confuse 'em?
(Do-won stares at him, bewildered)
Tae-goo: ... Fine, I'll decide. (He runs in a zig zag, dodging bullets. Do-won shakes his head in disbelief.)
Tae-goo wearing a diving helmet in the Ghost Market fight. He spends the fight running around trying to keep his balance and attempting to shoot Chang-yi's thugs wearing the heavy thing. Furthermore, the diving helmet proves to be very tight as well.
Tae-goo finally gets to the place where the treasure is supposed to be, and searches for it through a pair of wallet binoculars... only to find the end of Do-won's gun barrel instead.
Early in the film, when Tae-goo takes the map and goes up to rest in his room. Byung-choon and his thugs spot Tae-goo walking upstairs and hope to kill him and try and get the map. Unfortunately for them, Tae-goo hears their approaching footsteps and calls out, "Who is it?" and Byung-choon, on the other side of the door, accidentally reveals himself. It's his frustrated expression that's so funny.
Captured by Do-won, Tae-goo escapes, bolts out the door laughing madly... and notices Do-won and the other resistance fighters are right there.
Foe Yay Shipping: There's lots of fanart of Do-won/Chang-yi on Tumblr and DeviantArt.
There's a fair amount of Chang-yi/Tae-goo art on Twitter, mostly coming from Japan. Do-won/Tae-goo fanart exists but it's extremely rare.
Tear Jerker: The international ending is just depressing.
The last we see of Man-gil, he's mortally wounded and lying in Tae-goo's arms. We get the impression that he's not going to make it.
What an Idiot!: Byung-choon blowing his chance at killing Tae-goo and taking the map for himself, as mentioned in the funny moments above. He catches himself on his mistake, but it's too late.
Chang-yi's employer threatens him with a gun and rattles off on a monologue instead of just shooting him, allowing Chang-yi to kill him first. To put it into perspective, his counterpart Baker was defenseless and had the excuse of already being mortally wounded.