Dai is very gentle, to the point where it takes a lot to make him even a little annoyed. He is patient and appears to be slow-witted or even simple to others, often resulting in his being ignored by his fellow colts while growing up. This disheartened the young Dai and he consequently finds socialising difficult at times, finding solace in the peace of the garden and if he is in company, the number not exceeding more than a small crowd as his confidence developed. He is still a touch shy, but he makes an effort to overcome it.
As he grew up, he became curious and querulous to the world around him. He displayed, and sometimes still does, a great interest in subjects he knows next to nothing about, provided of course he isn't planning his crop. His own brand of intelligence and humour, akin to that of a serial bookworm, can often show itself in strange references to subjects that most ponies would headtilt at. He also acquired the trait of displaying a greater than normal respect for mares. His mother was most definitely the head of the household and even his father was inclined to defer to her authority. Consequently Dai prefers to defer to female authority as his mother (often simply referred to as 'Mam' or 'me mam') was a major influence on his growing up and future career choices.
Dai was born in Caerfilly, a wealthy agricultural and mining town founded by earth ponies. Dai's family, the Thunderhooves, were unusual in that they were unicorns who happened to share a skill in maintaining the land, but their acceptance into the community was slow and somewhat tedious. They settled in and soon became one of the biggest farming families in the area.
Dai is the youngest of four brothers and the smallest in stature. This meant he was unfit for most farm work and had to be put onto lighter jobs, such as planting, seeding and, quite often, herding the various livestock on the farm. Often he was mocked for his stature but he didn't mind the lighter work, finding his interest piqued more in the techniques of growing than purely hard work. He found the techniques of his brothers somewhat heavy-hooved and opted to seek advice from the neighbouring earth ponies to find more efficient ways of working.
With full support from Mam Thunderhoof, he began to acquire skills and friends from the earth ponies around, many willing to lend him a hoof with mastering techniques handed down for generations. Dai's curiosity became almost insatiable and he sought ways to help in return, using his developing magic to aid his own experiments. His growing use of magic became a concern lest it became too uncontrolled so he was sent to the school in Caerfilly, since his power was not enough to get as far as Canterlot's schools of magic.
He graduated with flying colours but Dai felt almost resentful his studies had taken him away from what he loved most; farming. His return was heralded by a gift from his parents, the family greenhouse that fallen into disuse since the larger scale agriculture was of more interest. It was his pet project, something he could use his magic on while still helping out at the farm at the same time.
Dai earned his cutie mark and his consequent nickname when he experimented on a patch of leeks to see if small doses of magic might work. Surprisingly, it did. The very first crop was a pair of leeks that somehow crossed each other slightly as they grew, earning Dai his cutie mark. It also earned him a new nickname, one that stuck: Greenhoof. He grew so used to the name that if he is referred to as Dai Thunderhoof, he sometimes doesn't respond.
His mishaps, unfortunately, were more known than his successes. His success rate is very high but his mishaps took on an epic scale. He entered the local Eisteddfod one year for the Young Gardener award but the few months before, he made the mistake of responding to the goading of a rival, aided in part by the offer of a small salt lick by one of the friends of his rival. He took the dare of making the biggest vegetable he could that could remain stable under high doses of magic and copious doses of a Caerfilly local plant, dragonroot. Dai used a tomato in his experiment but the result was disaster. As it exploded in the judges' faces, Dai slunk away and swore off any salt in the future, leaving victory to his rival. The next year, he did try again but this time came third with a giant marrow.
As Dai came closer to 20, he felt bored on the farm. He'd helped improve things so much that it could run by itself, although he still was required as herder to the critters on the farm. Once again, he was given a chance to do something interesting but this time his parents gave him the keys and location of a home in Ponyville, once a holiday home for the Thunderhooves, but in need of repair. His instructions were simple; he could renovate it, alter it, do pretty much anything as long as he reported back and was involved in the community. Given his natural shyness, Dai was apprehensive but the prospect of a new project excited him and he went away with a promise to write back often with the progress.
Dai's skills are best with anything and everything to do with the garden. While he does retain many typical unicorn magical skills, such as levitation, he prefers to utilise his talents in the garden and has sworn off using his magic for anything too showy or offensive to his nature. His level of magic is subsequently lower than most unicorns and held that way as he was quuite heavily influenced by the eath ponies around him.
His exception is his approach to hedge trimming where he likes to fashion the hedge into interesting shapes. His biggest effort in this regard is a perfect recreation of Princess Celestia in the back garden, complete with pastel coloured flowers to complement the flowing mane and tail. The flowers were an unintentional touch but he is so pleased with his efforts, he decided to attempt to create a Luna on the other side, updating her look after witnessing Princess Luna's more mature look upon Nightmare Night. To use his magic for artistic licence is his only exception to being showy.
He also has a talent for playing the harp, believing music to help plants grow better. His repertoire includes several ballads in his native tongue and some older Haylic classics. At one point he was part of the Caerfilly Young Colt Choir and his singing voice is deep but pleasant to the ear, with a more pronounced Halysh accent than when spoken normally.
Dai has a practical approach to any relationship. He never goes overboard with affection in public and tended to shy away from a direct approach unless he was sure that his affection would be returned. His romantic attachments were few. His first attempts were fumbling and clumsy and never went beyond foalish then teenage curiosity. Before he left Caerfilly, he had to end his longest running relationship with a weathermare due to work conflicts causing them to be too busy for much else. He remains good friends but since her promotion to higher ranks, she has been unable to contact him of late.
Since his move to Ponyville, Dai has settled in with Coaldust, finding himself quite comfortable in her company. She seems to have brought him out of his shell somewhat and in replies to letters Dai has sent back, Mam Thunderhoof has been nothing but supportive as well as glad the place is in good hooves. As comfortable as he is, he never makes a great deal about it but the idea of marriage and foals has invariably raised by Mam, something he hasn't given much thought to as of yet.
Familial relationships are more complex. Dai gets on very well with his parents still and takes pleasure in reading the letters from home as to what is going on back at the farm. His eldest brother is another matter. Owain Thunderhoof, later known as Stormy Thundersson for his art studio in Canterlot, was antagonistic at points with Dai and both could only be in the same room with some difficulty. Consequently, Dai almost never has any contact with him.