History
A brief history of the origins of Aikido
Daito-ryu Aiki-jujutsu 大東流合気柔術
Daito-ryu aiki-jujutsu was originally the unarmed combat method of the samurai of the Takeda clan and dates back around 900 years. Its lineage was passed down to Takeda Sokaku in the early 20th century. He decided to pass it onwards to one of his most gifted student, Morihei Ueshiba.
Aikido 合気道
Ueshiba mastered daito-ryu and started teaching it in the early 1920/1930. However, Ueshiba interest in the Omoto-kyoreligion led him to modify a lot of the hard techniques of daito-ryu into something softer and named his style Aikido. During that time, Ueshiba demonstrated his style to Jirogo Kano, the founder of Judo. The latter was so impressed that he sent one of his top students, Kenji Tomiki, to train with Ueshiba. Tomiki joined Ueshiba in the so-called Hell Dojo and was given a certificate of mastery (meiko kaiden) from Ueshiba. The first one ever to be given which was eventually translated into an 8th degree black belt.
Shodokan Aikido 昭道館合気道
After the second world war Aikido, in common with all Japanese martial arts, faced great difficulties. Tomiki focuses his efforts in bringing the art into universities. Tomiki, being a student of Judo, started to incorporate Kano's ideas of martial arts into Aikido. After years of work, Tomiki founded his own style called Shodokan Aikido. This is the style that the York club trains in. Currently, the head of the style is Tetsuro Nariyama, one of Tomiki's top students.
Other styles
• Aikikai, the organisation founded by Ueshiba.
• Yoshinkan, a hard style founded by Shioda and of Angry White Pyjamas fame
• Ki Aikido, a soft style founded by Tohei.
• BAB, the UK the Aikido umbrella organisation.
• And Many More...
There are plenty of sites on the Internet where one can learn more about Aikido (the way of harmony) but here are some suggestions: The Aikido FAQ is a good place to start, Wikipedia should be no surprise, and finally a StackExchange question site exists if you have question.