The Tsuba (or Toban as it was called in former times) holds a very important place in the accessories of a Japanese sword.
It serves to keep the user's hand from sliding up onto the blade of the sword, to counterbalance the weight of the blade and, to some degree, to protect the hand from an opponent's blade.
Apart from its practical function, the Tsuba symbolized the ideals and personal aesthetics of its owner. This becomes most apparent when one considers the position of the Tsuba, which it takes when its sword is being carried in the Obi. In this case the Tsuba is located almost in the center of the body and serves as an eye-catcher. The austerely and uniformly dressed Samurai hereby gains the opportunity to express his personal aesthetics and beliefs as well as to communicate his social standing.
Due to these characteristics, a large variety of Tsuba with very different forms and designs developed. They were able to serve all occasions a Samurai could encounter, be it a court visit or the battlefield.
In my opinion, it is the early iron Sukashi Tsuba, that particularly enriches and decorates the sword as the "Soul of the Samurai" and complete this weapon with a personal note of each of its owners. These early Tsuba are often mentioned as exhibiting a "quiet strength", which I think is a great description of their character.
The earliest Tsuba date back to about 400 AD and over time they became more and more subject to the artistic skill and design of their creators. Many different materials, shapes and forms were chosen to give them their final character.
This large variety of Tsuba, with designs ranging from the plain to the elaborate, the simple to the audacious, makes them a very fascinating and rewarding subject of study.