A century or two ago, Corwin was born to the Tunnelcarver clan in the deep gnome city of Blingdenstone. The Tunnelcarvers were famed for their doughty wardens and warriors. Together with their cousins, the famous Bissengulps, these two families formed the cornerstones of the city's defense. These champions watched over the dark corners of the earth, making sure their city was well protected from the dangerous beasts and predatory denizens of the Underdark.
Corwin was a weak and clumsy child, and he was also shy and meek. He was immensely gifted with a vivid and rich imagination; while his creativity and memory could not be questioned, this attribute was a double-edged sword in the Underdark. He was easily spooked and suffered frequently from nervous fits, brought about by the exciting and thrilling tales of his elders' exploits. (Take a rich storytelling tradition, a geographical proximity to aberrations and other monsters... add to that, a racial affinity for creating incredibly lifelike illusions... well.. growing up in the Underdark can be very scary for gnome children.)
Corwin admired the warriors of his family, and he secretly felt unequal and unworthy of the legacy and tasks laid out before him. The young gnome thus sought to compensate for his perceived flaws by running the roofs and tunnels of the city alone; he wanted to confront his deepest fears and prove to himself that he was not a weakling.
Using his sharp intellect, Corwin drew maps of the forgotten and abandoned areas of the city, and he liked to loiter in these derelict districts, and pretend to himself, as children are wont to do, that he was a mighty warden, who would watch over Blingdenstone and protect it from secret threats that only he could see.
It was during one of these secret forays, that Corwin's deepest wishes came true. As he was running the rooftops of Blingdenstone's abandoned warehouses, pretending to be an intrepid and dashing warrior, he happened to chance across a raiding party of kuo-toa, who were probing the defenses of the city, seeking to make captives of the deep gnomes as sacrifices for their dark god. In his excitement, the gnome child fumbled and was detected, and the fish-people gave chase to him.
As he was being cornered, Corwin was about to use his Ghost Sound power to misdirect the kuo-toa, but a sudden surge of courage inspired him to use the spell to sound an alarm, and alert the rest of the city. Thus, Corwin was captured, and the fish-men were about to feed him to their chuul pet; in the nick of time, a Tunnelcarver raiding party saved him from his piscine tormentors.
Corwin returned safely to his family, and was severely reprimanded by his elders, but they were secretly proud of his efforts. Corwin found himself profoundly changed by this experience; he felt much stronger and braver, and focused his efforts and energies into his craft, earning the respect of his peers (and more importantly, himself). He poured heart and soul into training himself; despite his best efforts, he was still not strong enough physically to be a good warrior, but he gained the confidence to contribute to the defence of his community. He used his knowledge of the tunnels and city streets, together with his mastery of illusion magic, to create architectural schematics and urban maps, which greatly aided the wardens of Blingdenstone in their coordinated efforts to protect the city.
Some decades passed; five, six, seven, who can tell? Deep gnomes care not to measure time in the way of the Large Folk. Time is time, and that is enough; Blingdenstone welcomed the renegade drow Drizzt Do'Urden through its gates, as a guest of the respected elder, the Most Respected Burrow Warden Belwar Dissengulp, and the gnomes, once they have gotten over their initial fear and distrust of the drow, quickly warmed to the unusual drow, and many were the friendships forged and formed.
However, this happy moment was not to last; the warbands of Menzoberranzan came searching for Drizzt, and these cruel elves brought nothing but fire and darkness with them. Although Drizzt was no longer in the city (having decided to leave Blingdenstone in an attempt to avert drawing the ire of his vengeful family upon the deep gnomes), the communities of Blingdenstone decided not to take the chance, and they made plans to leave the city en masse for the deeper tunnels, so as to avoid the bloody-handed drow justicars.
Thus, the city's inhabitants scattered, arranging to meet again when these troubles with the drow had ended. Like so many other deep gnomes, Corwin led a vagrant's life, travelling with his family from place to place. The once-proud Tunnelcarvers, who had defined themselves by their adherence to the sacred duty set down by Callarduran himself, became more and more dispirited, as they lost their sense of purpose and place.
Corwin missed the tunnels and warrens of his home, but tried to soldier on as stoically as possible, and wait for this exodus to end. During this time, Corwin honed his fighting abilities in fending off the monsters of the Underdark; despite his lack of talent and physical might, Corwin was able to devise a new and unique fighting style of his own, as he melded his military training with his ingenuity and natural gnomish mastery of illusionary and earth magic.
When the drow armies of Menzoberranzan later marched for Mithril Hall in the surface world, in their pursuit of Drizzt Do'Urden, the Bissengulp Clan summoned gnomish warriors from all the clans of Blingdenstone to fight against the drow. The normally calm and reserved deep gnomes leapt at the chance to avenge themselves against their hated enemies who had driven them from their beloved home. The Tunnelcarvers were no exception; Corwin joined his clan in battle, as he was eager to test and hone his battlecraft.
The allied army of dwarves, Northmen, deep gnomes, Silverymoon Knights, Harpell mages, and Luskan soldiers were able to splinter the drow armies and send them reeling back into their shadowy lairs. Victory was sweet, and the drow seemed to have learnt a painful lesson; they did not return to menace Mithril Hall, and the gnomes decided to return to Blingdenstone.
Yet the enmity of the dark fey, once earned, is not easily forgotten; the memory of their humiliating defeat festered in the hearts of the matron mothers of Menzoberranzan. They could not accept such a harrowing defeat, and the priestesses of Lolth summoned massive hordes of bebiliths, unleashing the spider demons upon the hated svirfneblin. Spies and assassins from Bregan D'aerthe were also dispatched to find and capture the gnomish warriors who had dared to throw in their lot with the defenders of Mithril Hall.
The resulting carnage was truly horrific; the pogrom of gnomes left only a few survivors, who were herded by the assassins of Bregan D'aerthe to Menzoberranzan, where they would become sacrifices to the yochlol handmaidens of the Spider Queen. Corwin was one of these captives, but he was deemed unsuitable as an offering to the demons, due to his imperfect physical form. Corwin raged and swore bloody vengenance against his captors, but to no avail; he watched and wept as the yochlol and glabrezu emerged from the Abyss to feast on the bodies and souls of his brethren and loved ones.
This outburst amused the sadistic drow, who decided to keep him as a conscious witness throughout the whole grisly process. Corwin's mind broke down from the strain of his helplessness and grief; the insensate, maddened gnome was then sold, like so many other victims of the dark fey, to the mind flayer allies of the drow. Corwin's broken mind was of little interest to the discerning gourmands of the illithids, and so he served them as a menial slave.
As the years passed, Corwin forgot his past, and a new childlike personality emerged, perhaps as a means of protecting his own mind from his traumatic experiences.