As a member of foxes, and Someone who has talked to many old and original members, I will say this. iG as well as Foxes are not the oldest clans. There were clans before us on forums and clan that made system clans before ours was created. History, as previously mentioned by Gamehendge. When the System clans were coming out, the devs wanted to beta test system wars. Since iG and Foxes was apart of the first ever dev war, the wanted iG and Foxes to beta this system. Reluctant at first, both clans agreed with the promise that they would get their perspective clans for free. (Pre-pwar era, so 10b gold was a lot back then) So both clans was rewarded. Now this caused a fuss on forums, the devs caved and then gave every forum clan a free system clan. That volleyed tensions back to Foxes and iG and to settle, the devs rewarded both clans with 120 roster spots. Some other old active clans that started in forums are, The French Knights and Chaos Reborn.
Threads were made and people signed up and the thread was edited to show who was part of the roster. The clans all talked there and congregated
iG and Foxes are the two oldest clans in the sense of clans as we know them today. However, before the mechanics of the clan system were put in place, there were forum clans, which weren't officially recognized in game but were still clans in every sense. If memory serves (don't hate me if I'm wrong) Elite Templars were the first forum clan. Also, so you know, iG and Foxes were forum clans enforce they were "real clans" per se.
Edit* Trust RKoS over me. He's been around longer and has first hand knowledge. Mine is all second or third hand.
I slightly outdate Sholron but am by no means the active historian he is. I didn't pop on forums until Nov 09. I think that was to join up with iG. I was asked to sign in because I was in the second system war and was farming an alt of Trueplayer for 48 hrs for unloading on me. Apparently iG seemed to think I was the kind of jerk they wanted around. Before that I saw iG and Foxes hating on each other in WC. There was no Clans so you couldn't click a clan. You could go on forums and join one. Invalance Alliance, iG, Fox, and maybe 2 or 3 more were early 09. IG had a big start as their players came from another game as a team. That's sort of what formed the clan system. Since they were such a group to be reckoned with Foxes and Chaos formed for their own protection or as foils to the evil iG. This is as far back as I remember, but let's take it all with a grain of salt. Corinthian, or a few others outdate me and have better memories. They could trump my history here.
I thought it what white knights or something like that, I know iG and foxes were up there. There's a thread called a KaW timeline that has the correct answer