Oh, gee, Cardell. In some ways your questions are easy to answer and in other ways, oh so difficult. Difficult mostly because many of the folks I'm going to mention don't play UO anymore.
If I had to restrict myself to mentioning just one person, it would easily be Ed/Silk from KDL. I met him on Baja at a time when I was pretty much on my way out the door because most of my friends had left the game or had announced they were in their last weeks of playing. He had just come back from being away from UO for a few years and I noticed him a few times hanging out at his house on Baja that was near one of my houses. One day I wandered over just to say hello and before I knew it, he had talked me into helping him tame some new pets for his tamer. During the next week or so, he discovered I was somewhat interested in learning to PvP and suggested I give factions a try with a thief. So before I knew it, I was training up a thief/trap remover, not knowing what a painful experience it would be to train up Remove Trap.
We started out in CoM and the first sigil I ever stole was from the TB base. I'm not even sure who was in TB at the time. Could have just been Ed's doing to have those sigils there. LOL But before long, he had switched us over to TB and next thing I knew, we were joining KDL, who had just arrived on Baja from Napa Valley.
Ed was absolutely the most dedicated faction thief I've ever met. I was absolutely in awe of how organized he was about managing the sigil, trap and guard placement, and many other aspects of defending a base. When KDL transferred to GL, he also kept the entire guild supplied with potions. As good as KDL was before we joined them, I think Ed/Silk was absolutely key to their success on GL.
I also have to mention Da Trav, the KDL guild leader, and Joy who also helped run KDL. I used to enjoy the heck out of listening to both of them in Vent and watching them PvP. Both had red dexxers (most every character in KDL was red) and we were in TB at a time when the guard zone in Brit was very much a factor in faction fights. Trav kept pretty tight control over the group when we were guarding and you didn't often see or hear about someone in the guild off running around solo. It was pretty much get yourself into the base NOW, call targets, cross heal, get in another channel if you're distracting everyone with your chatter, and everything else that you need to do to be a successful team. KDL also had a fairly hard and fast rule that they killed any nonguilded TB first and asked questions later. That didn't mean KDL never took on new people. It did and from what I understand, many of the people I met when they got to Baja and then moved on to GL were people they had fought against on other shards. Talos is a good example of that. We ran up against him on Baja and he was so darn good with his thief and his tamer that we got him to transfer over to GL and join KDL there. Coke/Remat, Danny, and Poo were folks that joined KDL on GL too. One of the things I learned from Trav that's stuck with me over the years was that being in factions didn't mean you had to be a jerk to everyone else. I rarely (and I mean rarely) saw anyone in the guild talking garbage to the enemy. I distinctly remember Trav saying that the only person in the guild who really had the right to talk bad to anyone else was Agent Smith. And if you played at the time, you'll know why he said that...Agent Smith was pretty darn good. I'll also never forget learning from Trav that it isn't necessary to always, always, always have control of the towns. Sometimes it is a good idea to let someone else get them and have the ability to put up horse breeders and get war horses. If you don't, then pretty soon, who will be left to fight against?
Some other KDL folks that were generous with their faction and PvP knowledge were Agent Smith, Darma, Road Rash, and Rat. I truly miss talking to Rat and Road Rash.
I must also mention Digitalis/Kylas. Although I never had the chance to play against him on Baja, I remember reading his thoughtful and knowledgeable posts on Stratics quite a few years ago and am always thrilled when he shows up here and provides his perspective on things.
And last but not least, I must mention my current guildmates: Poo, Romus, Nex, and Q. Although we're not anywhere near the force that KDL was, if it weren't for them, I'm sure I would not still be hanging in there in factions. Somehow these guys inspired me to make even more trap remover/thief characters and actually try to do some PvP, something neither Silk or anyone in KDL was ever quite able to talk me into. It has been an absolutely amazing experience to hang out with the four of them these last couple of years, and Talos too at times, and gradually get my feet wet with other aspects of PvP and hanging out in Fel. They've kept me logging into UO on a pretty consistent basis, inspired me to make far too many characters to effectively keep track of, and have become wonderful friends in the process. And because of them and the YAD "world tour of factions," I've had good reason to settle in on quite a few other shards and meet up with quite a few other crazy factioneers.