Gan Williams was born together with his siamese brother Tavis Williams. Their parents an unnamed Vienamese woman and Walter Williams.
Walter Williams, a second lieutenant of the US army, met a Vietnamese woman while he was assigned in Vietnam for several months until he was assigned elsewhere. Later it was found that the Vietname woman was pregnant and was ostracized for it. She left Vietnam and later found the fabled land of Hsuan in the North China Sea. There she was accepted and gave birth to siamese twins Gan and Travis Williams. Chan Ti performed a ceremony and applied jade herbs and ancient incense and he was able to separate the children. However, after the process, it was discovered that the children were different. Gan possessed the power of thunder while Tavis that of the lightning among others. However, their powers apparently became unstable and Chan Ti said that they need the blood of their father to cure their condition. Thus began their search for their father.
Their search brought them to Saint Louis but apparently, was told that he left already. Their bouts of instability brought them to the attention of the army and the Teen Titans. After calming down, they received information that their father was in Maine to which they immediately went. Searching for their father and their unstable powers sometimes caused them to act irrationally resulting in their second bout with the Teen Titans. The battle ended when Wonder Girl arrived with information that their father disappeared after an accidental laboratory explosion. Thinking their father dead, the Williams lost interest in the battle and surrendered. Cyborg suggested that they go to S.T.A.R. Labs where they might find a cure for their condition.
S.T.A.R. Labs however, was not able to cure the brothers. Losing hope, the brothers tried to leave but the Teen Titans came to stop them from leaving. Raven then offered to use her soul self to find the whereabouts of their father and it was discovered that he was being held captive by H.I.V.E.. It was then discovered that their father is actually an alien who crash-landed in Vietnam and is being experimented by the H.I.V.E. Under the H.I.V.E.s control, their father attacked them and the Titans, and the brothers were forced to kill their father. Using the blood from the corpse of their father, S.T.A.R. Labs was able to stabilize the brothers powers, curing them. Thereafter, the brothers went home to Vietnam.
Thunder, as well as Lightning, was shown not too long afterward to have begun working with S.T.A.R. Labs again. When Atomic Skull, who had been getting treatments under S.T.A.R. Labs in his civilian identity, began to wreak havoc at S.T.A.R. Labs, Thunder and Lightning defended the place and rescued the lab technicians on hand. Following that event, during a time when Frances Kane was hypnotized into attacking the twin brothers in her Magenta garb, Thunder and Lightning defended against her assault and fought her until she regained her senses.
- Psychic Link: Gan has a psychic link to his twin brother Tavis. The two can speak to one another telepathically and sense when the other is in danger. The two brothers often speak to each other through this telepathic link rather than speak verbally.
- Sound Manipulation: Gan has shown the ability to project concussive blasts of sound, predominantly by clapping his hands to release the sonic energy (playing off the word "thunderclap").
- Superhuman Strength: While his exact levels of strength are uncharted, Gan has shown the ability to lift great sums of weight, once supporting a massive piece of lab equipment from falling on several lab technicians.
- Lightning Bolt: Thunder's brother Lightning has the ability to create a solid bolt of non-damaging lightning that the brothers can use as swift air-transportation.
- Although this character was originally introduced during DC's Earth-One era of publication, their existence following the events of the 1985–86 limited series Crisis on Infinite Earths remains intact. However, some elements of the character's Pre-Crisis history may have been altered or removed for Post-Crisis New Earth continuity, and should be considered apocryphal.
- Williams is 18 years old. 
- He was conjoined twins with his brother.
- 20 Appearances of Gan Williams (New Earth)
- 3 Images featuring Gan Williams (New Earth)
- Quotations by or about Gan Williams (New Earth)
- Character Gallery: Gan Williams (New Earth)
- Thunder at dccomics.com
- Thunder and Lightning (comics) at Wikipedia.org
- Thunder & Lightning article at Titanstower.com
- Thunder bio at the Unofficial Guide to the DC Universe