Clans are groups of people who fight amongst themselves and generally look down on the general Netbattle population. They target younger players and have been known to solicit sexual favors in exchange for a higher status in the clan. Many new NetBattlers, regardless of their background, are suspectible to clan recruitment because it provides security for them. In order to join a clan, you usually have to defeat the leader and then swear allegiance to the cause and your clanmates.
No one is certain when the first clan started, but the first clans started in 2003. Most clans were based on the teams in the Pokemon games, i.e. Team Rocket, Snagem, etc. They would use teams from the video games and forfeited if you used standard teams against them. Many people have claimed that Atq was the first clan, but there is no proof that they were the first clan. All that is certain is that the first clans were very divisive and short-lived.
The Peak of Clan Success
Clans reached their peak in late 2004, with as many as 15 english-speaking clan servers up at once. Some of these clan servers even reached the top position on the registry, which was no small feat during those times. While Tafop and BH were down on the registry in December of '04, Zero Hacker's clan emerged as the top server. This was remarkable because he was only 10 years old and had a limited knowledge of how to run a server. He was unable to maintain this success once Smogon debuted on NetBattle and eventually left in mid-January. A few clans broke into the top 5 servers, but none ever threatened Smogon's dominance at the top.
A Change in the Guard
Until 2006, clans had traditionally been English-speaking, so it came as somewhat of a shock when a number of Br clans popped up on the scene. These clans united to take control of NetBattle as revenge for the treatment they received from the general population. For the first time in NetBattle history, there was widespread discrimination against English-speaking people in foreign-language servers. The anti-Anglo sentiment died down in 2007, as many people left NetBattle and Brazilian servers outnumbered English-speaking servers by a ratio of 2:1 in the top 10.
Present-Day State of Clans
Clans are still around on NetBattle and will be until its eventual end, but not nearly to the extent that they once were. The methods of recruitment include promising instant influence in the clan and guides to battling. Unlike past clans, leaders play a small role in the operation of a clan, leaving the day-to-day operations in the hands of their members. This approach has produced better battlers, but clan members are still left unexposed to the metagame for the most part. It isn't until a clan member cuts back on their time in a clan that they improve substantially, but many are conditioned to stay in their protective groups and so never realize their full potential.