For as long as I've been playing MMOs I have played solo when levelling my characters. Sometimes though one meets extraordinary people on their travels. So much so that I even married one but that is a different story. I am referring to just the friends I have met.
My first MMO, like many, was WoW. I was a complete and utter n00b (except for my paper and pen RPG background of course). I don't remember exactly how I fell in with Hillman. At that time I was 34 years old and going through a painful divorce. Hillman was a barely 21 year old man working in a bakery. He was so funny, so full of charisma and forever dancing (I don't know if the actual player was dancing. I assume not but Hillman, the paladin, was). We would wander through the game world trying to kill dragons we had no way of defeating or jumping off Teldrasil to see if we could survive. And killing pirates. A lot of pirates. Some of my fondest memories of WoW are with Hillman the dancing paladin. He doesn't know it but he saved my life. But, as you do in life, we went our separate ways. I am sure he is still afk in Ironforge.
After I moved to the UK, I started playing MMOs on EU servers. Again, in WoW, questing in Zangermarsh I met yet another paladin by the name of Digdug. He was in every zone I was in for a couple of days so finally I started talking to him. He was rather quiet but we eventually started hanging out. That was probably almost five years ago and we still play together. We have levelled several toons together through multiple games. Much to his detriment he lets me lead wherever we go. I have a certain knack for running through many many mobs to see if we can survive. I think the record was 25 wasn't it, Ian? He gives me the number count after and we have a laugh. He tolerates my jumping and flipping in combat because I think I am a ninja. He is forever getting lost or pulling the wrong mob but somehow through incredible teamwork we always work it out.
There are several through many games that have impacted me in some way or another (for good or ill) and hopefully there will be many more.