Beidomon was a male channeler in the AOL who worked with Mierin (aka Lanfear) to create the Bore. The question is, was he somebody important to the story, or was he just some poor grad student?
We know that he wasn't one of the male Forsaken. In the Guide, we learn all of their original names, and what they did before turning to the Dark Side. None of them were named "Beidomon," and none of them did the kind of research into the One Power that Lanfear did (see section 1.1.1).
It has been suggested that LTT was Beidomon, based on the fact that he and Mierin were lovers at one point, and upon a few scanty quotes. One of these is from [TEOTW: Prologue, Dragonmount, xv]: "him who brought the Shadow... they named Dragon." The other is [TEOTW: 4, The Gleeman, 44]: "I will tell you of the end of the Age of Legends, of the Dragon, and of his attempt to free the Dark One into the world of men." However, this idea does not hold water. For one thing, LTT was named "Lews Therin Telamon," not "Beidomon." Secondly, we know from [Guide: 6, The Female Forsaken and the Darkfriends, 62] that LTT dumped Mierin "some years before the drilling of the Bore." Thirdly, LTT was a politician/bureaucrat, the leader of the Hall of Servants, not a researcher [Guide: 3, The Age of Legends, 31]. Furthermore, the bits about him that brought the Shadow being named Dragon are from the late Third Age and the Fourth Ages, long after true details were confused and forgotten.
The best guess we can make, based on the scanty evidence we have, is that Beidomon was just some guy who was part of Mierin's research group, who assisted her in the actual drilling. The Guide [Guide: 6, The Female Forsaken and the Darkfriends, 63] tells us that Mierin was "fortunate to be one of the few to survive the backlash that destroyed the Sharom and most of the Collam Daan."
Jordan gave us more details about Beidomon in one of the Tor Questions of the Week archived by the 13th Depository:
Beidomon was a male Aes Sedai, and a research genius, who believed that they were onto something great. The drilling of the Bore itself caused great damage, and Beidomon, Lanfear and others involved were blamed for that. Once it became clear what had actually happened, the opprobrium increased, and Beidomon sought obscurity, finally committing suicide when he was unable to achieve it. Everyone knew his name, and what he had done. He had nowhere to hide.