Keroro

Keroro is the titular character of Keroro Abridged (obviously) and is the Sergeant and First-in-Command of his self-titled platoon/klan (despite being only the second-highest in rank) and as such, is in charge of Keron's invasion of Earth and the most motivated out of any of the others to do so. He's also characterized as being extremely egotistical and as such, a complete and total jerk to everyone else around him, wanting nothing more than to just do his job.

History of Characterization
While he is changed very much from the character from the original series, he hasn't changed very much throughout the Abridged Series. From the beginning, he was written as being extremely egotisical and an ass to everyone else he meets. While that isn't very different from the personality in the original series he is much more intelligent and competent than the original character and his fellow platoon members in the Abridged Series; though, in Episode 0, he was portrayed as being more of an idiot, something that now only happens whenever he's around Dororo.

Relationships
Tamama - Despite Tamama being a random and stupid character, he and Keroro generally get along pretty well (especially when Keroro has his random spurts), as Tamama generally seems to accompany him the most, along with Giroro.

Giroro - Having been friends with Keroro all of his life, he has the biggest relationship with him, out of any of the other characters. Due to gaining his child-like personality, he takes up? Tamama's? role of intensely admiring Keroro (even to the degree of having an ambiguous attraction to him). Despite this, Keroro seems to not particularly care about Giroro and criticizes him numerous times throughout. Also, Giroro and Keroro's roles are a bit swapped, compared to the source material; in that Giroro could care less about invading Earth, while Keroro, on the other hand, is much more focused on his job, due greatly to his boost in intelligence.

Kululu - They don't seem to have a particularly bad relationship with one-another, given that they don't interact with each other very often. So far, they are two of the most intelligent characters in the show and are probably the only pair who can hold an intelligent conversation with each other... if Kululu stopped being so sexual for 2 seconds to actually make an intelligent conversation, that is.

Dororo - They don't have much of a relationship, but compared to everyone else, Dororo has more reactions with Keroro than anyone else in the Klan. Keroro (and the rest of his Klan members) seem to think that Dororo is actually one of Keroro's childhood friends, Zeroro, despite his constant claims that say otherwise. Dororo doesn't seem very interested in any of them, not even bothering to remember their names (usually calling Keroro a different name every time). In addition, Keroro tends to act like an idiot whenever he's around Dororo most of the time ("Dororo is so much of a straight man that he makes Keroro seem stupid by comparison... to the point where he actually is.").

Fuyuki - In a situation similar situation to Tamama, he gets along very well with Keroro, despite being extremely dumb and random.

Natsumi - Due to Natsumi's aggressive demeanor, they both seem to dislike each other. Multiple times Natsumi has threatened Keroro, to the point where he doesn't really care anymore. Despite this, Keroro has briefly lusted over her on occasion.

Angol Mois- Keroro seems to use and abuse her; taking advantage of her emotions for him, insulting her numerous times, and not really caring about her safety, despite her literally being his niece (stemming from her calling him "Uncle" in the show).

Narrator - Keroro is one of two characters that the Narrator interacts with (the other being Kululu). Just like with everyone else, Keroro's always an asshole to him, usually forcing the Narrator to influence the direction of the show in his favor, much to the Narrator's annoyance.