These were the guys who saved the world.
According to the Gearwrights, they are ancient; older than current civilization. There is, however, very little evidence of this fact. As far as current history is concerned, a dwarf named Parilus either started or restarted the guild. Since he disapeared after the construction of the first city mech, no one has been able to ask him for any proof.
Membership into the guild is highly restrictive. Only the most skilled coglayers are ever even allowed to become apprentices, and it usually takes years to even gain a full membership. The central advantage of being a full member is access to their Master Repository, the collection of all knowledge known to the Gearwrights.