- "You have to learn to push through the pain. If we all sat down every time it hurt, this country never would've been built... What happened, bad pileup at cheerleading practice?" - Adam to Lana Lang, Asylum
Adam had bright, blue eyes and dark brown hair.
He first met Lana and it was clear to see that he had a very persistent, yet emotionally distant, personality. He also has had emotional "roller-coasters" and is easily offended. By the end of his time on the show he was sociopathic due to the lack of serum and his want to live.
As Chad Nash, he learned martial arts, computers and piano. He died from a liver disease, but was resurrected by Lionel Luthor and Dr. Lia Teng using the Lazarus Serum. He was renamed "Adam Knight" and sent to Smallville to become Lana Lang's best friend and learn everything she knew about Clark Kent.
Adam met Lana Lang in physical therapy at the Smallville Medical Center after being trampled by a horse. Adam provoked her to stop playing the victim and to make an extra effort. He told her that he had lost his parents in a fire and he was receiving treatment for injuries received when he tried to save them.
Adam and Lana started to grow closer and hang out together. Adam displayed some unusual talents that raised Lana's suspicions.  He decided to stay in Smallville and Lana rented him an upstairs apartment at the Talon.
Chloe Sullivan saw Adam injecting a mysterious substance and thought that he was a drug user. She snooped around his apartment and found a vial, which she had analyzed and discovered he was taking a serum made from unusual blood platelets.  Lana discovered that he was identical to Chad Nash, who had been dead for five months, but Adam refused to talk about it. 
Lana did some snooping in Adam's apartment and discovered a journal of notes proving that he was spying on her and Clark. She tried to evict him, but Adam refused to leave, so Lana asked Lex Luthor for help, but before Lex could do anything, Lionel collected him. Disappointed that Adam had alienated Lana, Lionel declared that he was no longer a participant in his research program. Dr. Teng was horrified by Lionel's decision and snuck Adam the drugs he needed to survive.
Adam was in pretty bad shape when Lex found him, but when Lionel closed down the lab, Dr. Teng gave Adam the last dose she had and let him go. Furious that she didn't have any more serum, he strangled Dr. Teng to death. When the rest of the lab staff discovered his crime, Adam killed all of them and made his escape. He returned to Smallville to obtain the serum that he left in his apartment, but needed Lana to take him to the storage facility where she sent his things. 
Adam used Chloe to discover Lana was hiding out at the Kent Farm and threatened to kill Jonathan Kent and Chloe if Lana didn't come with him to the storage facility. When they searched his things and found that all the serum was gone, Lana attempted to escape and Adam ran after her with a gun. He tried to kill her for lying to him, but she really didn't know where the serum was. Clark arrived just in time to take the bullet meant for her, in full view of a dying Adam. Adam suddenly realized why Lionel sent him to spy on Clark. Just before he died, Adam admitted that Lionel had sent him to watch Clark. 
- When Adam Knight first appeared, there was internet speculation he was actually the Smallville version of Bruce Wayne, based on the combination of the name of one of the actors to portray the character, Adam West, and one of Batman’s nicknames, "Dark Knight", as well as the obvious details of his status as an orphan and his skills in such diverse areas as martial arts and computer hacking. The crew stated it was never their intention to reveal Adam Knight to be a young version of Bruce Wayne.
- The creative team decided to bring the character’s storyline out of the romantic path and into a "thriller Pacific Heights direction". According to Alfred Gough, the character’s storyline degenerated into a science fiction story and when that occurred, they decided they had to wrap it up quickly.
- Adam Knight appeared in 7 episodes, which tied him in number of appearances with Dr. Harden, Grant Gabriel, Gina, Jeff Hage, and Faora (clone) as the 10th most frequently seen recurring characters in the series after Jor-El, Nancy Adams, Brainiac, Emil Hamilton, Ethan Miller, John Jones, Nell Potter, George, and Helen Bryce. Adam, Dr. Harden, Grant, Gina, Jeff, and Faora are the most frequently seen recurring characters tied with each other in the number of episodes they appeared in.