Okay. I'll preface this with Gallant's conception as a character. I wanted to do two things with him as a character - one, write what I know (I know a lot about the military); and two, challenge myself to create an alicorn OC without any Sue traits. This second part is where the real challenge lies - can an alicorn be developed well enough to be a good OC?

Note that the following is describing hin just before my first fic with him starts.

Name: Gallant Charger
Title: Commander (Thirdprince*) Gallant Charger of Westfold**
Nicknames: 'Third' to his siblings, 'Gal' to a select few.
Gender: male
Age: 67 (during S3)
Species: lesser alicorn***

Coat colour(s): sandy brown
Mane and tail colour(s): a few shades lighter than black.
Mane and tail design: cut short, often messy.
Eyes: Golden-brown, standard design.
Cutie Mark: Blue kite shield with two swords crossed behind it
Adornments/Accessories: none
Cutie Mark Symbolism: the shield symbolizes his overriding desire to defend others and the swords symbolize his skill at arms - the two together represent violent skill controlled and contained by a desire to protect.

Personality: ENFP, apparently. Intuitive, driven by emotion, good at improvising, but very borderline for introvert/extrovert.

Strengths: He's intuitive and creative, but not spontaneous. He's devoted a lot of time to honing his skills, physical, magical and mental. He's humble without falling into self-depreciation. He's cultivated a commanding presence and has a natural tendency to take a leader role.

Weaknesses: he's extremely arrogant, though it mainly shows up as irrepressible confidence rather than condescension. He's stubborn to a fault, and rarely slows down to explain his plans. But his two biggest weaknesses are emotional.
He is extremely closed-off emotionally, and keeps his feelings hidden at all times unless he's with a select few friends - he hides all his actual emotion behind a coolly confident, classically heroic, stoically inspiring façade he calls his 'mask'. He is also quite isolated - he has exactly six ponies he will drop his 'mask' around, which tends to leave him quite distant from others even if they think they're his closest friends. He doesn't seem very approachable.
He also tends to rely on others for his emotional stability. The few ponies he allows to know him are extremely important to him - he grows to rely on them and feels he failed them if they are hurt.

Likes: He spends his off-hours reading. He's fond of escapist books and has a liking for history. He also enjoys flying, and will sometimes go thermal-riding for fun. He takes great pride in his combat skills.

Dislikes: He has a 'trigger' - if any harm comes to a child, all bets are off.

Job: Commander of Westfold****

Family: Queen Cherryblossom of Westfold (mother, lesser alicorn, deceased), King Goldtop (father, concept name, earth pony), Firstprincess Royal Grace (sister, lesser alicorn), Secondprince Stone Thrower (brother, lesser alicorn), Fourthprince Wild Card (brother, lesser alicorn)

Friends: Major Rapid Burn, Westfold Royal Guard***** (girlfriend, unicorn pyromancer), Pilot Light (Rapid Burn's daughter, unicorn filly), Mint 'Minty' Tulip (unicorn mare, Royal Grace's hoofmaiden, family confidant), Major Silver Bolt, Equestrian Royal Guard (pegasus crossbowmare, old Academy friend).

Enemies: vary from story to story.

Birth: born in Riverside Hospital, Westfold.

Childhood: Gallant spent most of his youth with only his family and tutors. He would often go adventuring through the palace with a wooden sword his brother had made for him, fighting off pirates or ninjas or dragons or or space aliens or whatever else caught his attention at the time. Once he was old enough to understand it his parents began teaching him things like diplomacy, governance, how to inspire others to follow your lead, how to make moral choices and then how to own the consequences of those choices. Because he was tutored at home and didn't really go outside, Gallant had a fairly solitary childhood until his cutie mark appeared.

Cutie Mark Story: Gallant had started heading down to the markets with one of the palace's seven staff whenever they needed to buy something. While they stocked up he'd wander off and meet new ponies. On one of these trips he saw a colt being backed against a wall in an alleyway by two other school-age ponies. He intervened, but all he was able to do was smack one of the bullies on the nose with a wooden sword. Both he and the other colt were in danger now, and there were no nearby adults to help. Instinctively, Gallant cast a shield spell he'd never used before. It was enough to attract attention, and the bullies ran off. Gallant's mark emerged then and there.

After Cutie Mark: Gallant became friends with the pony he'd saved, a streetwise pegasus named Fast Lane. Gallant nagged his parents into letting Fast Lane be tutored with him, and from then on the two were inseparable. The two balanced each other out - where Fast was always eager and cheerful, Gallant was more sedate and relaxed; where Fast was irresponsible but fun-loving, Gallant was reliable and sensible; Fast would get them into trouble and Gallant would get them out of it. Gallant found the military appealing from a young age, and Fast decided to enlist as well. Unfortunately, Fast had been pushing the bounds of the law for a while and had a few misdemeanours. In his last year at the Academy, Fast got hit with a felony charge and Gallant couldn't do anything - he was barred from service and Gallant was posted to the coast. The two never reconnected.

Career: Gallant entered Westfold's Royal Navy (Fleet Air Arm) at the age of eighteen, joining the coastal patrol squadron called 'Longshore Flight' as a midshipmare. He rose to the rank of lieutenant-commander and occasionally took command of a small team of specialists to work as a 'warlock hunter', tracking and capturing magical criminals. He was eventually selected for the Westfold SAS 'Sabres', combination infiltration and combat soldiers tasked by Westfold Intelligence. He was gradually promoted through commander to captain. He went on multiple missions with the Sabres, both high-stakes small-team commando operations and more deceptive missions closer to a spy novel than a military op. He was eventually selected for high command and was rotated into the Westfold Royal Guard for two years mandatory training as colonel. He then spent two years as the incumbent Commander's second before ascending to the position himself. He's been Commander of Westfold for six years.

Other:
A few small but important notes to help untangle my worldbuilding:

*Thirdprince: Westfold is an elective monarchy (the Triumvirate choose the monarch). The line of succession get 'first dibs', because of their upbringing and training, but any citizen may apply for consideration and any applicant must be a 'worthy citizen' (i.e. an academic will need a certain level of degree, a soldier will need a certain rank, a tradesmare has to submit a masterwork to a guild, et cetera), including the royal family. The monarch's children are titled with a number indicating their place in the line of succession, i.e. Firstprincess, Secondprince, Thirdprince, et cetera. Unlike other nations, simply being a prince/ss is not a noble title and confers no power whatsoever, being superseded by any job title.

**Westfold: the Kingdom of Westfold is an independent nation on Equestria's west coast, founded around 1300 years before the show by those fed up with Canterlot's sycophantic, self-important, backstabbing and ineffectual nobles. They have no nobles, instead using a system of mayors to bring issues to the monarch's attention directly.

***Lesser Alicorn: A rare breed of pony, a lesser alicorn is born when a foal has equal genetic ancestry from all three breeds (there's some random chance and some natural magic involved, too). They have both wings and a horn, but lack the super-equine power, stature or capabilities of a High Alicorn or an Ascension. Lesser alicornism in inherited, but there is some leeway (courtesy of the magical element). The most well-known lesser alicorn line is the Westfold Royal Family, tracing their line to Earl Grey the First. Lesser alicorns live approximately three hundred years, spending the majority of their lives in their physical prime.

****Commander of Westfold: the highest ranking soldier in Westfold and a member of the Triumvirate. Selected by the chiefs of staff (the five-star general officers from the army, navy, air force and royal guard, plus the Commissioner of Westfold Intelligence), the Commander technically holds viceroyal diplomatic status and the military authority of (in human terms) a six-star general.

*****Royal Guard: Westfold's Royal Guard is a separate service branch to the Army, Navy or Air Force, and they cherry-pick candidates from other service academies. They run Westfold's defences and bases, perform small-scale combined arms ops and operate the Gendarmerie (military-run police force).

I'll attach other character sheets I've made for him, a little later in his timeline. One and two.