Fong initially chose the pseudonym "Threshold of Pain", which meant being able to withstand enemy fire and suffering. However, as many games had an eight-character limit and the truncated "Threshol" did not sound cool, he went with "Thresh" and liked the meaning of it which was to strike repeatedly. Today, Fong never uses his pseudonym for casual online gaming, as it has been adopted by a large number of impostors.
A key to Thresh's success in gaming tournaments is not only due to his reflexes, but also because he made use of far sight, counter-intuition and tactics. His opponents called his intuitive ability "Thresh ESP" for his skill in anticipating what they were doing. For instance, he would not necessarily pick the most popular or strongest characters, but rather lesser known ones from which he would practice how to defeat the popular ones. In 1 on 1 Quake deathmatch, keys to his success include making effective use of weapons and powerups, particularly the rocket launcher, to never aim at the enemy directly and target the nearby wall instead. He also paid attention to sounds and used them to deceive his opponent. Also crucial to his success was his understanding the level so he could "control" vital items, using timed runs to repeatedly hoard it from opponents, such as the rocket launcher and armors.
The crowning highlight of his gaming career was at the Microsoft-sponsored Red Annihilation tournament in 1997. He and "Entropy" (pseudonym, real name unknown) emerged from a crowded field to face off in the Quake level E1M2 "Castle of the Damned", where Thresh defeated Entropy 14:-1. In the post-game interview, Fong said that the score was not an adequate reflection of their skills, acknowledging that once he had the Yellow Armor controlled, this made it very difficult for Entropy to fight back. (The Yellow Armor, which has 150 armor points and absorbs 60% of damage, gives an immense advantage in survivability especially in rocket duels.)
In his gaming career, Thresh went almost undefeated and won many tournaments he entered over a five-year span, and did it in a variety of games including Doom I and II, Quake I, II, and III, and StarCraft.
Using his prize winnings and endorsement money which was rumored to be in the six figures, Fong and his brother Lyle started GX Media, the parent company of Gamers.com, FiringSquad, and Lithium Technologies. Dennis was the CEO of the company while Lyle was the CTO; together they grew the company organically and profitably to a 100-person company.
In 1999, Fong, as the CEO of GX Media, raised over US$11 million dollars in financing from CMGI and led the company to the position as the leading web portal for games. Fong's Ferrari was parked in the lobby of the GX Media offices and the company threw a party at the Playboy Mansion during E3. In 2001, Gamers.com was bought by Ziff-Davis, and various other parts were spun off into separate entities. One of the entities, Lithium Technologies, is now run by Dennis' brother, Lyle, and is a leading CRM company based on social technologies.
In 2007, Fong founded Raptr, a software client and social network that keeps track of what games you play, keeps them up to date and gives gaming suggestions based on you and your friends' gaming history.