I apologize for the length, but I wanted this to be as comprehensive as possible. I figured too much detail is better than not enough. :)

Please note that the Attributes, Feats, and Skills are based on the D&D system (or KOTOR, if you're more familiar with that game).

Name: Kieran Nimh
Nicknames: Kieran Halfpaw, (the) Halfpaw
Derogatory Nicknames: (the) Dragon’s Toy, (the) Hamster, (the) Scratching Post
Race: Rat
Height: 6.5” or 14cm
Weight: 8 oz or 226.8 g
Fur: Black, with a silver belly, throat, and chin
Eyes: Pale blue
Class/Occupation: Scout

Stats

Strength: 12 (above average)
Dexterity: 16 (superb)
Constitution: 16 (superb)
Intelligence: 10 (average)
Wisdom: 10 (average)
Charisma: 10 (average)

Feats

Armor Proficiency—Medium: Kieran is capable of wearing the Medium and Light armors of the Thorn Valley Guard, but cannot wear the heaviest armor without further training.
Master Unarmed Fighting: As a Scout, Kieran received extensive training in the rodent equivalent of the martial arts. Finding that he enjoyed the training, he continued through the training regimen until reaching the top. He is among the top unarmed fighters of the Thorn Valley Guard.
Weapon Mastery—Melee Weapons: Given the covert nature of many scouting missions, expertise in melee combat is a must.
Ultimate Resilience: Kieran trained himself to enhance his already considerable natural resistance to pain and injury. This greatly enhances his survivability in a combat situation.

Skills

Healer Adept: Kieran received training as his unit’s assistant combat medic and has since studied more under the watchful eye of the unit’s medic to improve his skills.
Smith Novice: Kieran knows how to make simple repairs to his armor and weapons.
Scout Adept: Through his training as a Scout, Kieran has learned how to move quickly and quietly. This training is accentuated by his natural dexterity, making him far better at sneaking around than a rat his size has any right to be.

Equipment

Padded Doublet: Worn under the armor, this item is designed to help insulate the wearer and provide some protection against minor blows.
Camouflage Light Scout Armor: Designed more to keep the user from being seen or smelled than injured in combat. Intended only for use on scouting missions.
Camouflage Cloak: Enhances the user’s ability to sneak around undetected.
Medium Plate Battle Armor: The heaviest armor most Scouts are trained to wear. Intended for use in combat and the standard uniform of Scouts when on duty at posts outside the main colony.
Wrath (bastard sword): The paw-and-a-half sword Kieran obtained after losing most of his left paw.
Ruin (dagger): Standard-issue dagger of the Thorn Valley Scouts.
Uniform: The standard-issue uniform of a soldier of the Thorn Valley Guard, worn mainly when stationed in the colony proper.
Haversack: Kieran’s pack for when marching between duty posts.
Civilian clothes: Just what they say they are.
First aid kits: Exactly what they say they are.
Armor repair kits: Exactly what they say they are.
Apartment keys: Exactly what they say they are.

(He obviously does not carry all this all the time!)

Physical Description

Kieran’s fur is jet-black, though his stomach, throat, and underside of his lower jaw to the tip of his chin are silvery-white. His eyes are a pale, almost icy, blue. Where his fur is black, Kieran’s scars stand out as a charcoal gray. Where his fur is silver-white, the scars stand out as a snowy white.

The gene therapy affected Kieran most physically, greatly increasing his size, strength, dexterity, and overall resistance to injury and disease. He stands a full head and shoulders above Justin, though he is nowhere near as tall as Brutus. His strength is above average, though not spectacular, but Kieran makes up for this with his stunning speed and agility. Kieran is also one of the most resilient rats in the Thorn Valley Guard and is well known for aggravating broken bones and other injuries because he thought they were only “minor.” These attributes made Kieran an ideal candidate for the Thorn Valley Guard.

Intellectually, however, Kieran got gypped. While certainly not stupid, Kieran’s intellect is only at the average for the colony, which made becoming his unit’s assistant combat medic more difficult than it would have been for a bit brighter rat. The gene therapy also left his trusting and basically guileless nature alone, leaving him lacking in the cunning department and also rather easy to manipulate by rats such as Jenner.

History

Kieran does not remember much about his life prior to NIMH and therefore assumes that he spent most, if not all, his life as a test specimen there. Unlike most everyone else in the colony, Kieran feels almost no fear towards the humans. His name, in fact, was taken from the lab technician who injected him with the experimental serum. Kieran views this technician as a father figure, which doubtless contributes to his bizarre attitude towards humans. Without a true family of his own and not knowing the surname of his “father”, Kieran changed the lab’s acronym to his surname. He felt it fitting, given how many years of his life he spent within its walls. Most of the other members of the colony find his last name odd; some find it absolutely disturbing.

During the events chronicled in The Secret of NIMH, Kieran found himself supporting Jenner’s plans to steal from the farm family. However, Kieran’s support was based primarily on his desire to interact more with humans. He knew that Jenner would give him that opportunity and, being rather naïve, did not think Jenner willing to kill to get his way. He learned that the hard way after Nicodemus’ murder. Kieran has yet to forgive himself for being taken in and, however indirectly, being a part of Nicodemus’ death. Another consequence of this is that Kieran is now deeply suspicious of anyone who wishes to upset the order of things or introduce radical changes within the colony. This paranoia is rarely a good thing, and often leads to heated arguments between him and those he is close to.

Personality

Kieran is a solitary rat with few good friends and a very small ring of close acquaintances. He feels socially awkward, and his attitude towards humans does not help him fit in with the other members of the colony. It goes without saying that he is single and, while desiring companionship, doubts that anyone would ever consider becoming his mate. Despite this, he is a devoted friend.

His obsession with studying humans and learning all he can, despite the risks to himself, is the source of his many nicknames. Among his friends, he is generally referred to as “The Halfpaw” because he lost most of his left paw to Dragon on one of his excursions to the farmhouse. Showcasing his odd sense of humor, Kieran traded in his standard-issue long sword for a bastard sword after recovering from his injury. “A paw-and-a-half sword for a rat with a paw and a half. It’s perfect,” he said. Those who aren’t so fond of him refer to him as “the Hamster” because his tail was reduced to a stump on a subsequent visit. Those that really cannot stand the rat call him “the Dragon’s Toy” or “the Scratching Post”, in reference to the many scars he bears from these trips to the farmhouse.

However, despite the names, the reputation, and the scars, Kieran refuses to stop. The notes he has gathered have proven useful on occasion (such as learning when the farmers planned to summon exterminators to deal with the feral rat problem in the barn and fields), leading him to believe that his excursions are actually intelligence-gathering missions for the good of the colony. This belief has allowed Kieran to delude himself into taking greater risks, supposedly “for the good of the colony”. Since he only engages in these trips when on leave, his superior officers are powerless to stop him. They can only hope he doesn’t get himself caught, eaten, or otherwise killed between Thorn Valley and the farmhouse.

His obsession with humanity has led him to become obsessed with some human habits and mannerisms, as well as with some of their forms of entertainment. Through considerable effort on his part, he has procured scattered pages of novels, news magazines, and other printed material. Kieran keeps these tucked away safely under his bed in his quarters. His ultimate dream is to obtain an entire, in-tact novel and read it, though he doubts he will ever succeed in this.

Kieran is a dedicated soldier and one who would not hesitate to sacrifice himself to save another…or so he likes to think. That situation has yet to arise, and he is secretly glad of it. His head doubts his heart’s conviction to sacrifice himself to save one of his comrades or a civilian from harm. He is, however, a superb fighter (as evidenced by the fact that he’s survived multiple encounters with Dragon) and has a good sense of how the battle is proceeding and which of his comrades is in need of help. He has proven himself a valuable asset to his unit and has earned the grudging respect of his fellow scouts. A few even count him as a friend.

When not training, Kieran can most often be found perusing the notes from his excursions obsessively. Kieran wants to compile these notes into some sort of reference book, a sort of definitive work on humanity (or at least the humans of the farm house), but lacks the writing skill necessary to do it well. He has started the project many times and almost completed the first chapter before discarding his work as worthless and abandoning the attempt. He invariably swears he’ll never try to write the book again, but always winds up making another attempt at some point in the future. Kieran knows he needs help with the writing, but can’t work up the courage to approach any of the colony university’s professors for help.

Kieran holds the Brisby family, and Jonathan especially, in very high regard. Mice they might be, but Jonathan died in a mission to put Dragon to sleep, while Nicodemus himself met privately with Mrs. Brisby and agreed to help move her family to safety. Kieran finds himself slightly in awe of the mice because of their brief but close contact with Nicodemus, and greets them (even the children) with a respectful bow on the rare instances that he meets them.