—Moiraine Damodred (The Shadow Rising, Chapter 17)
He is fairly old, and has a gnarled face, shaggy white hair, and blue eyes. He is tall, with stooped shoulders. He wears a cloak that is described by Bran al'Vere as having more patches than cloak and more colors than you can think of. It is also described as quite thick, having odd, baggy sleeves and big pockets. His snowy hair and long mustaches make him appear older than he probably is, given his spryness. He is frequently portrayed as smoking a pipe.
Thom's age is not specifically given in the novels. He is said to be white-haired, but still attractive enough to attract considerably younger women such as Dena, whilst Elayne notes that he is still handsome. At one point Morgase muses that Thom was "twice her age" during their relationship, presumably in 984-85 NE when Morgase was 27 (turning 28), which would have made Thom around 54-56 at the time (and therefore about 70 at the start of the series) but at another point Thom is described as being "in his prime" at that time, suggesting a younger age.
Robert Jordan's notes on Andor attempt to be more precise, saying that Thom is about 19-20 years older than Morgase. This would had made Thom in his late forties during his relationship with Morgase and about 60 or 61 when the main series events begin. The contradictory information is presumably why Thom's age was not canonised in The Wheel of Time Companion.
Not much of his early life is known, except that he was Bard to the young Lady Morgase of House Trakand. He helped her ascend to the throne of Andor, became her Court Bard, and was renowned in noble circles in most nations. He thwarted Taringail's plan to kill Morgase and killed him instead. He and Morgase became lovers. Somewhere during this time, Thom discovered his nephew and only surviving blood kin, Owyn, was being pursued by the Red Ajah because he could channel saidin, but he was too busy with his duties to Morgase to seek him out.
The issue of Owyn returned later and Thom disappeared to help him, but he had waited too long: Owyn had been gentled by the Red Ajah as part of the male channeler pogrom, and had subsequently died alone. When Thom returned, Morgase was angry with him for leaving - a fight ensued, and Thom said she was a spoiled baby and a tool of the White Tower. He accused Elaida for the role he suspected the Red Ajah played in the circumvention of White Tower law, Gentling Owyn without returning him to the White Tower first, something he had counted on taking long enough to give him more time. He left, barely dodging the execution block.
Thom is hot-headed, but generally kind and considerate, though he nurses a hatred of the Red Ajah and a distrust of all Aes Sedai , following their treatment of his nephew. A great player of Daes Dae'mar, Thom is able to sort out what is important among the information he gathers and which is just lies. He assisted Matrim Cauthon in rescuing Moiraine from the Tower of Ghenjei, and is currently her Warder and husband.
Escape from the Two Rivers
With his Bardic talents and his experience in the Andoran court giving him more than the requisite skills, he became a gleeman and journeyed across the land, performing in inns and villages, sometimes for pay, sometimes just for supper and a bed. He just so happened to arrive in Emond's Field late on the same night Moiraine Damodred arrived, and was present on the very next night when Trollocs attacked. After the four young people decided to leave for Tar Valon with Moiraine who by then had revealed herself as Aes Sedai, he went with Rand al'Thor, Mat Cauthon, Perrin Aybara, and Egwene al'Vere, fearing that they would succumb to the same fate Owyn had by following Moiraine; he felt he had to repay his failure to help his nephew. When the company was later split up after their foray into Shadar Logoth, he ended up on Bayle Domon's ship along with Rand and Mat. He seemingly sacrificed his life to protect them from a Myrddraal in Whitebridge; while he did not die, the encounter did leave him with a permanent limp. Actually, he was Healed by an Aes Sedai who managed to save his life, but not prevent the limp.
Thom later ran into Rand in Cairhien when the young man was making his way to Falme. Soon afterward, Thom's apprentice and lover Dena was murdered by men in the employ of King Galldrian Riatin. In a suspicious turn of events, the king was murdered hours later; Thom may or may not be the killer, as even his own statements on the subject are ambiguous. It is strongly hinted that he is the killer when Elayne offers him a pardon for any crimes he may have committed in Cairhien, to which Thom replies "How did she know...".
Depressed, he left the city and made his way to Tar Valon, where he began drinking heavily. It was here that Mat reentered his life after escaping from the White Tower. They rejoined the company in Tear after the Fall of the Stone.
Thom uses his knowledge of the Game of Houses and his ability to collect information to aid Rand. He manipulates the Tairen High Lords or passes information to Rand on who to look out for.
Moiraine requested that Thom take care of Nynaeve al'Meara and Elayne Trakand as they journeyed to Tanchico. She informed him by the Three Oaths that he would survive Tarabon, that they would meet again, and that she would then provide him with the names of the Red sisters who gentled Owyn, as well as the one who gave the order to have him gentled on the spot.
After Tanchico, he and Juilin rescued the two young women when they were dosed with forkroot by Ronde Macura. They then joined Valan Luca's Traveling Show, where Thom performed as a fire-eater and juggler. They accompanied them on their trip to Salidar where afterwards they were sent by the Salidar Six to scout around Tarabon for a time before returning again. Mat arrived in Salidar soon after Thom returned but Thom is told to stay away from him. Thom then went to Ebou Dar with Elayne, Nynaeve, and Mat to search for the Bowl of the Winds.
Thom and Juilin stayed with Mat after the Seanchan capture Ebou Dar and Mat was injured, during which time he planned some scheme with Beslan Mitsobar against the Seanchan. He also used the excuse of playing the harp to sneak into the room of one of Tylin Quintara Mitsobar's maids. He helped Mat escape with Tuon.
He, with the rest of Mat's group, joined up with Luca's Traveling Show as a cover while they fled from Ebou Dar.
It was later revealed that Thom knew of Moiraine's fate after her battle with Lanfear and that her rescue would require Mat's help. This comes from the letter that Thom received after her "death," in which she details some of what she saw when visiting the three rings in Rhuidean.
Traveling with the Band
He accompanied Tuon Athaem Kore Paendrag and Mat to a hell in the town of Maderin. While in The White Ring he brought the news that the entire Seanchan army was after Tuon, claiming she was an imposter. As they were all leaving the hell, they were spotted by Darkfriends intent upon killing Mat. Thom protected Tuon while Mat engaged another group behind them. Here Thom witnessed Selucia's fighting ability. At the end of the fight Thom professed to not remember seeing Selucia fight at all.
Furyk Karede entered the Band's camp, looking for the return of Tuon. He asked to speak to Thom, having him confused for being in command of the Band and the hatcher of a plot to take Tuon to the White Tower.
He rode with Mat into the cursed village of Hinderstap and was attacked by the crazed villagers when nightfall descended. The group only just managed to escape the village and wait the night away before entering the village again at daybreak to find everyone back to normal. Later he met with Mat, who was planning how to the approach Trustair, the next village along after Hinderstap. He was present when Verin Mathwin arrived in camp and informed Mat that saidin has been cleansed.
Thom watches with Mat, as Teslyn, Joline, and Edesina leave for the White Tower. He then rides with Mat into Caemlyn to meet with Queen Elayne. After a pleasant greeting with her, Elayne offers him a proclamation to become a proper court-bard of Caemlyn. He promises to think on it. Thom is with Mat when they finally catch up with Perrin again in The Happy Throng in Caemlyn. There they discuss the feats they have carried out and the respective wives they have married. Mat tells Perrin about possible assassination attempts and to try not to sleep in the same tent every night. Mat then discusses his plan to rescue Moiraine from the Tower of Ghenjei.
—Thom Merrilin 
Tower of Ghenjei
After the Band set up camp in Caemlyn, the gholam attacked Mat. During the fight the gholam threatened to kill Thom. After the attack Mat insisted on Thom sleeping in the city in a different tavern each night. He meets with Mat and Noal in lower Caemlyn to discuss their strategy on how to retrieve Moiraine from the Tower of Ghenjei. Thom provides a variety of musical instruments for the "music to dazzle" verse.
Thom traveled to the Tower of Ghenjei with Mat and Noal in order to confront the Finn and rescue Moiraine. He was the one who endured the burning mist trapping Moiraine in the Chamber of Bonds, pulling her free. After escaping the Finn's world, Thom and Moiraine announced to Mat their plans for marriage. He is also bonded by Moiriane as her Warder.
The Last Battle
Thom tags along with Moiraine, when she enters the discussion between Rand and all the other monarchs of the land at the Field of Merrilor. There Moiraine manages to quell all argument against Rand, leading to all the rulers signing the Dragon's Peace. He is with Rand, when he stands just outside Shayol Ghul, testing whether the Dull dagger works. Thom decides to guard the entrance to the Bore rather than enter with Rand, Moiraine and Nynaeve. He kisses Moiraine goodbye and watches them as they enter the Pit of Doom. There are many channelers wearing Mask of Mirrors posing as, among others, Cadsuane Melaidhrin. He killed at least five intruders, the last one being Jeaine Caide, and dumps the bodies in a hollow not far from his position. He uses his time guarding the passage writing a ballad telling Rand's tale and the Last Battle. He compares several words to each other to determine which one he should use.
After killing the Black sister, he starts writing everything down before he is forced to flee because the battle is nearing its end. When the Bore is closing he grabs Moiraine who has rushed out of the cave, keeping her from falling over the cliff.
A man, not Thom, juggling fire and the White Tower. 
Similarities to Merlin
- Both Thom and Merlin advise very important people in their respective series (Rand and King Arthur), and after certain events both Thom and Merlin cease to advise their former pupil.
- In some legends, Merlin is the son of an Incubus; a male version of the Succubus known for its abilities at manipulation, much as Thom plays the Game of Houses.
- The persona of Merlin is also linked to a woman named Nynaeve (one of a number of Lady of the Lakes with similar names), and is eventually trapped in an enchanted tower by her.
- Merlin was known for the ability to shape-shift, changing his appearance to disguise his identity. Thom is an excellent spy with the ability to blend into any situation without appearing out of place.
- Ironically, Thom makes a reference to it himself. When speaking of how history may not remember him correctly. "Thom Merrilin. Not a gleeman — but what? Who can say? Not eating fire, but breathing it. Hurling it about like an Aes Sedai.” 
The Eleventh Ball
Rodel Ituralde tells a story about an unnamed Court Bard in Caemlyn, who must be Thom, juggling in front of an unnamed Daughter-Heir, who must be Elayne. Having reached the point of juggling ten balls, he yielded to the clamor of the crowd, and his assistant tossed out an eleventh.
- That last "ball" wasn't actually a ball at all. It was some kind of Illuminator's trick; once it got halfway to the bard, it flashed and gave off a sudden burst of light and smoke. By the time our vision cleared, the bard was gone, and ten balls were lined up on the floor. When I looked around I found him sitting at one of the tables with the rest of the diners, drinking a cup of wine and flirting with Lord Finndal's wife.
In the television series
- The Eye of the World, Chapter 1
- The Eye of the World, Chapter 4
- The Fires of Heaven, Chapter 19
- The Eye of the World, Chapter 35
- The Eye of the World, Chapter 2
- The Great Hunt, Chapter 25
- The Great Hunt, Chapter 34
- The Dragon Reborn, Chapter 31
- The Shadow Rising, Chapter 4
- The Shadow Rising, Chapter 17
- Knife of Dreams, Chapter 10
- The Gathering Storm, Chapter 27
- The man is most likely Thom's nephew, Owyn, who was Gentled by the White Tower. Likely juggling fire is symbolic of his channeling, and the White Tower of his Gentling.
- The Shadow Rising, Chapter 19
- The Gathering Storm, Chapter 10