Tom grew up in Plains territory with Ava and Laughing Jack. The three siblings shared a psychic connection that allowed them to link their minds as if they were one. This allowed them to know what the others were doing, even if they were miles away.
When the siblings all went their separate ways, Tom set up a small shop on the border of the Plains and Ralad territories on the Plains side of the border. His symbol is a lightning bolt.
City of the Rats
Lief, Barda, and Jasmine saw a sign pointing to Tom's shop when they were travelling through the Ruby north. They arrived at the shop a day after escaping from Ichabod. Since Tom was away from the counter at the time, Barda commented that it would be easy to steal what they wanted.
To prove this, he tried to take a lantern, only to find he could not lift it or remove his hand. Tom then arrived and, after letting Barda go, was more than willing to show them around his shop. Lief and Barda were in awe at the many strange and unusual wares Tom sold, though they were unable to buy most.
As Lief and Barda prepared to buy their goods, a scar-faced man entered the shop and bought a self-coiling rope for less than what the companions were offered. Lief noticed it was because he drew the symbol of the Resistance on Tom's counter. Tom saw Lief's recognition, caught Lief's eye, and passed him a jar of fire beads and a pipe that could blow bubbles of light. For their free gift, he provided them with a container of Water Eaters (though only when Lief asked.)
As they prepared to leave, Lief and Barda found Jasmine petting some of Tom's horses. Barda then asked if they could return the goods they'd bought so as to buy the animals, but Tom maintained his no return policy. He was willing to make a trade for Lief's sword or cloak, but was shot down. Jasmine then brought out the money she had taken with her from the Forests of Silence, inciting Tom's greed. While Tom did not sell them the horses, he did give them Muddlets to ride instead. As a final word of advice, he warned the companions to take the left path on the approaching crossroad. They believed this was as a warning not to go to the City of the Rats, but rather it was because the Muddlets belonged to the city of Noradz and bolted when they smelled home.
Later, after the companions escaped Noradz in a cart full of food, they found themselves back at Tom's shop. He greeted both the Ra-Kacharz and some approaching Grey Guards as friends. He knew where the three were hiding, but rather than reveal them, he distracted the Guards with talk and sent the Ra-Kacharz back to Noradz. While hiding, Lief, Barda, and Jasmine learned that the horses he had were for the Guards, as the food cart was to be taken to Del to feed the Shadow Lord's servants in the palace.
Tom later spoke in private to the companions, telling them to go while it was safe. The three of them chastised him for pretending to aid the Resistance while really being an ally of the Shadow Lord. Tom laughs and explains to them that, like his signpost, he is the same whichever way you view him. All he really cares about is business.
Despite the companion's trust in Tom being shaken, his goods saved their lives several times on their way to the City of the Rats.
Return to Del
Nanion and Manus stopped at Tom's shop on their way to Withick Mire, and delivered Doom's message to all members of the Resistance.
Cavern of The Fear
After Barda found the city of Noradz deserted, he sought out Tom, knowing the shopkeeper would likely know what had happened to the city and its inhabitants. Tom explained that the Ra-Kacharz drove the people to the Shadowlands a few days prior to the Shadow Lord's defeat.
Isle of the Dead
Tom knew through his bond with his brother that Lief, Barda, and Jasmine had a run in with Laughing Jack. When Manus stopped in his shop on his way to Tora, Tom gave him a jar of fire beads, some peppermint candy, and a seemingly blank note for Lief. Manus gave these gifts to Lief when he met him in the Dreaming Dunes, where, by the fire caused by the beads, Tom's note revealed itself in invisible ink. He explained to them about his sister, Ava, and how to gain a boat from her with the candies. As a disclaimer, he listed the price for all the items—to be repaid at nearest convenience.
Tom is a tall, lean man who often wears a hat. He is lanky, long-limbed, and long-fingered. One of Tom's most notable characteristics is his wide mouth and mocking smile, traits he shares with his brother, Laughing Jack. It was through their similar smiles that Lief realised they were related.
In the anime, Tom is a purple-eyed, grey-haired, bespectacled man who wears a white shirt, a pink-red vest, a round hat, and brown trousers.
Tom is a man of business, and does most things for money. Always eager to make a profit, he is sometimes greedy. While he offers a "free gift for every customer", he only gives it when asked. Tom likes to think he is a neutral party—like himself, his shop's sign looks the same from either side. Although he may pretend to be impartial, Tom is as much of an enemy of the Shadow Lord as any other person in the Resistance. He has a good relationship with his sister Ava, and feels a sense of responsibility for his brother Laughing Jack's acts of evil. He encouraged Lief, Barda, and Jasmine to ask for Ava's service, sending them a pack of Peppermint Fancies and a jar of fire beads (with a disclaimer of the price of each item, to be repaid later).
Given Tom's wares are all obviously magical in some way, it is possible Tom is some kind of magic user or at the very least knows how to craft magical items. This theory is supported by the fact that Plains people breed strange beings, and Tom does have the curious gift of having his mind linked to his siblings'.