HISTORY
This self defense martial art was developed in Tokyo, Japan in 1942 by Morihei Ueshiba. Ueshiba's development of this self defense martial art came after he underwent a sort of spiritual transformation.
He was already trained in a form of jiu-jitsu (another kind of self defense martial art), called yagyu shingage ryu. After catching scarlet fever, he had to recover his physical strength, so he practiced this martial art. When the Russo-Japanese war broke out, however, he had to enlist and was sent away. The experience was good for him, though, because he brought back with him several different self defense methods and approaches to various kinds of martial arts.
When he returned home, his martial arts teacher made him a master instructor. Ueshiba wanted to learn other self defense martial arts though, so he traveled to different parts of Japan. He quickly learned the martial art of daito-ryu, but he wanted to learn a self defense, martial art that was more harmonious, rather than military-based.
When his father died in 1920, Ueshiba became psychologically unstable. He looked for a spiritual guide and he found one. A Shinto priest named Deguchi took him under his wing, and taught him the many ways of meditation and philosophy.
One day, while he was meditating, he came upon a vision. He had been walking to get a drink when the ground around him started to shake; in front of him, a stream of vapor shot out of the ground. Instantly, Ueshiba was bathed in a gold liquid, and he felt like a feather-- weightless. He could hear voices, but only saw birds when he looked around him. It was at this pinnacle during his vision that he realized that the universe and he were inter-linked, and that the foundation of martial arts should be based on a universal kind of love that brings about harmony and mental energy.
After this revelation, Ueshiba returned to Tokyo and opened his first martial arts and self defense dojo in 1927, thereby incorporating what he had learned from the other martial arts and basing it on his new-found philosophy and understanding of the universe and the world. It was in 1942 when Aikido was officially named a new self defense martial art.

PHILOSOPHY
The name "Aikido" means "the way of harmony," which embodies the basic belief of this self defense martial art. This martial art is a method of self defense; the master does not attack unless he/she is attacked. The martial art was formed from Japanese Zen philosophy, which holds the belief that the center of meditation or the source of one's mental energy, or ki, is in the center the body. This martial art teaches students to harness this power through exercises, breathing and meditation.
Mainly, students of aikido will go through extensive martial arts training to tap into their ki, and to develop a physically fit body and mind. As in some of the other martial arts, the main teachings emphasize that it is better to not resist if possible.