Nikolaj "Niko"

Personality

Positive Traits
Caring/Protective - Those that Niko loves will find that he is very vocal in expressing that care and love. He has a protective streak for them, wanting to keep them from danger.
Eager/Ambitious - Niko is always seeking out opportunities to improve his strength, and to help Rocket Hideout to thrive - his achievement as the youngest ever Platinum Recruit was a testament to that ambition. He hopes to one day become the General of another branch of the organisation.
Responsible - Niko always strives to carry out any of his duties, and will often do things that weren't assigned to him, just to have them done.

Neutral Traits
Judgemental - Niko's high expectations for his own performance often result in him judging himself as insufficient when circumstances don't go as planned. 
Civil/Polite - In his childhood, Niko was a rude young Pokémon, and he has learned to move past that, instead facing the world with civility and politeness. He can still mouth off someone if they've frustrated him enough, but he tries to treat people with the benefit of the doubt.
Lonely/Withdrawn - Due to being abandoned by his mother at a young age, during a particularly traumatic event involving Darkrai, Niko has trust issues, and will often pre-emptively distance himself from possible friends in fear of them hurting him/leaving him later on. Persistent-enough Pokémon can get through that shell, as shown by his relationships with Tone, Otto, and the rest of the Polyfam.

Negative Traits
Demanding - Niko's high expectations sometimes expand to cover others alongside himself, asking that those around him fulfil their own responsibilites with the same enthusiasm that he does.
Impatient - Niko never quite learned the virtue of patience, often getting frustrated when duties are not completed on deadlines.
Aggressive - Niko's protective streak can get aggressive when anyone threatens his loved ones or disrespects his authority as a Platinum-Rank. Luckily the second cause is quite rare lately due to him now reaching an age where Pokemon are more likely to respect him based on age, as opposed to when he was a young teen and already Platinum.
Defensive - Niko is defensive regarding his Rank and the age at which he reached it, painfully aware that many Recruits thought he was only rising as fast as he did because his father was the General - thinking he hadn't earned his place. 

Biography

Nikolaj, or Niko as he is known to just about everyone, was born the only son of Tseng, a Mightyena/Espeon, and Dasani, Persian/Umbreon. Niko was born as a Meowth/Poochyena/Persian. He had two sisters, Rory and Illyana, and was close with both of them. Some might have called the trio joint at the hip. As a very young child, Niko respected his father, but he absolutely adored his mother. Dasani and his sisters were his entire world, and nothing would change that. The moment he was old enough to officially join the organisation he had been born into, Niko jumped at the chance alongside his sisters, excited to make his parents proud. As the only son of the General himself, Niko felt a lot of pressure to perform well and not screw up, so he put a great deal of effort into being the best recruit that he could be.

For the first year or two, this continued. Niko was an anxious child, often over-performing in his tasks out of a worry that he wouldn't do well enough. He was self conscious, seeing judgemental glares from all around - how could a kitten as small as he was be useful? But he kept doing, persevering in his duties and even excelling in some cases. Despite his successes, Niko still found himself lashing out at others whenever they doubted his abilities, stubbornly pushing him into working harder and harder - and perhaps too hard. Dasani did her best to temper Niko's ambitions and doubts, but she couldn't be there all the time... and soon wouldn't be there at all. 

During a situation where Darkrai was infesting recruits' dreams and causing them to fall asleep and not wake up, Niko was one of the unfortunate victims of the Pitch-Black Pokemon's curse. When he woke up, Dasani was gone, having taken Rory along with her. Niko was heartbroken by this event, and, not having the emotional maturity to do anything else about it, threw himself into his duties. 

He began taking on more and more small missions from the Commanders, neglecting anything related to a social life. This incredible dedication to work helped him rise from Bronze Rank to Silver, and eventually to Gold. He would occasionally get along with another Recruit, but never well enough to actually know how to interact with them outside of commander-assigned missions. He still got along well with Illyana, knowing he didn't have to prove himself to her. His sister would accept him as he is no matter how much he succeeds or fails, but he didn't trust that anyone else would act the same.

Then Rory came back. Niko was now well into his teen years when the youngest of the triplets waltzed through the doors of the Hideout, explaining all the adventures (good and bad) she'd been up to in her time away. Niko continued pushing himself, albeit to a lesser and more healthy degree now that Rory was back and able to notice when he was overdoing it, and soon enough he was awarded with the Platinum Rank - the highest height a regular recruit can attain. 

Some years passed. Tseng retired from his General position, leaving it to a bubbly Vaporeon-mix named Dottie. With his father's retirement and intention to focus more on his family, Niko feels as though he has finally gotten slightly out of the spotlight. He appreciates that. He started opening up, and has definitely lost some of the hard edges he used to have. He still had to deal with Pokémon who think he's only reached the heights he has because his Dad was the General, so he's still rather prickly, but at least there are some mons who believe that he got where he is due to hard work, grit, and determination, and not just because of nepotism. 

After years of hard work and training, Niko finally achieved evolution during a training battle with his dad, evolving into a Persian/Mightyena/Espeon. Soon after, Rory and Tseng left, causing some heartbreak for Niko. Eventually, Niko's friend, Whysp, encouraged Niko to move past his childhood crush on a now-departed Deerling-mix named Penny, encouraging him to pursue Otto and Two-Tone. It was a successful move on her part, and Niko joined the relationship. 

Their polycule was expanded over and over, as Clath, Canvas, Bitz, Noodle, and Sarun arrived one by one and two by two. The only one of these Niko ended up directly dating was Canvas, but he was still happy to have people around him that he cared for.

Then something else happened. After nearly a decade of absence... Dasani returned. Niko was cold to his mother at first, but after patience and several long conversations, they bonded as Mother and Son and formed a new parental bond.