Through the mid-90's, Glassjaw shifted through numerous other members and recorded a handful of demos. The two most notable members, vocalist Daryl Palumbo and guitarist Justin Beck, who was initially their drummer until 1998, were part of this first line-up.
They planted their seeds in 1993, when their members were just 14. Their origins lie in Long Island, New York. The history of Glassjaw is certainly a detailed and lengthy one. This is not to discount the influence of their forefathers, Big Black, Fugazi, Drive Like Jehu, Unwound, etc., Glassjaw were just one of the first bands to solidify 'the shape of punk to come' in the new millennium. Perhaps in addition to At The Drive-In and Refused, Glassjaw are the single most important band of their era to impact their genre, and still are today.
Try listening to any post-hardcore band that came after 2000, and the influence is apparent. Within the realm of post-hardcore, Glassjaw are undoubtedly one of those bands. In every genre, there are a small handful of bands/artists that can be seen as 'defining'.