Seal Team Six, the elite US military team that killed Osama bin Laden, was created in response to the botched attempted rescue of American hostages held inside the US embassy in Iran in 1980. The embarrassing episode, when eight American servicemen were killed, illustrated the need for a dedicated counter-terrorism team capable of operating with the utmost secrecy.
The team was labelled Number Six to confuse Soviet intelligence about the number of Navy Seals teams in operation at the time. There are apparently only two other specialist teams in operation. The members of Team Six are known as "black" operatives and exist outside military protocol. Its missions require the direct approval of the US President.
Source: http://www.independent.co.uk/news/world/americas/black-ops-team-born-after-botched-iran-hostage-rescue-2278031.html
