Urahara Kisuke
Under his carefree, unshaven, and laid back facade is a more meaningful character that is maybe one of the most vital parts of Bleach. He is the manager of Urahara Shop where Rukia buys her equipment and a former shinigami. Living for over two hundred years has helped him create a network of connections that allows him to recieve the latest news, confidential or not, from the other world. He may be kind hearted and always wearing a smile on the outside, but when it's time to get down to business, his face is wiped clean of all expression and his heart hardens, making him impervious to failing. He is Ichigo's life line to Soul Society, and as such, a major player in the world of Bleach.
Aside from running a seemingly illegal wares shop, Urahara is all knowing and wise of the surrounding events and it would appear that he keeps close tabs on Ichigo, Sado, and Inoue. After collecting Inoue and Sado from the ground just after their inner abilities were revealed, he calmly explained to them Ichigo's role in the situation. Due to his hasty collection of shinigami powers and his lack of basic training, Ichigo allows his spirit energy to overflow randomly into the immediate area, thus influencing other souls. Realizing the problems that this may cause later on, Urahara takes Ichigo under his wing after he sees him being cut up by Kuchiki Byakuya on a mission to place Kuchiki Rukia into custody. The grueling training begins in a newly constructed underground training facility after a brief warmup fight against Ururu, in which Ichigo is thrown around like a rag doll. Taking this chance to further the training, Urahara Kisuke severs the saketsu connecting Ichigo's spirt and body, and beginning the process of becoming a hollow.
Although his teachings may have been unorthodox, this was the fastest and most efficient way to train Ichigo in only ten days. Under his supervision, the rookie shinigami fought off the hollow inside of himself and was able to release his shinigami soul at will. Now running out time, the senkaimon set up by Urahara to enter Soul Society was ripe for use, but he decides to stay behind and instead appoints Yoruichi to take the lead. Ichigo, Sado, Inoue, Ishida, and Yoruichi enter the senkaimon and reach Soul Society, ending his direct involvement in the rescue of Rukia.
He is a man of many faces and mysteries, but Urahara Kisuke is best known for showing up when you need him most. It would seem that he is a puppeteer, always watching from the sidelines, and setting up pieces to a puzzle that he knows will be of use later. Whether his motives are selfish or selfless, he is Urahara Kisuke, Tenchou of Urahara Shop and an indespensible ingredient in the saving of Kuchiki Rukia.
The Shinigami
Urahara is the former captain of the 12th Division of the Gotei 13 in Soul Society. It is unknown yet who his vice captain was. Not much is known about his time in Soul Society but by other shinigami's reaction to his name alone is a clear clue that Urahara was a respected shinigami. This could also mean that for the last 100 years, by word of mouth about the former captain, Urahara has left behind an intimidating impression of sorts on the younger shinigami.
Urahara was also the founder and president of the Research Institute of Technology. Here Kurotsuchi Mayuri, the current 12th Division Captain, is the 2nd president.
Exile
Urahara is an intelligent man and an exceptional inventor but unfortunately it was one of his inventions that led to his exile 100 years ago. Urahara created a special and dangerous gigai, an artificial body which shinigami can use in the human world. This gigai was completely undetectable. More importantly, it devoured the spiritual power of the shinigami. By using the gigai, the shinigami would would never recover their power, their coordination with the gigai diminishes and the konpaku (soul) eventually becomes powerless.
Hou Gyoku
Urahara also created another dangerous mechanism. This was called Hou Gyoku. Hou Gyoku is a mechanism that could transform a hollow into a shinigami and a shinigami into a hollow. Every shinigami has their limit that can't be passed but there was one way to surpass it and that was to become a hollow. Urahara knew that Hou Gyoku was dangerous, especially if the wrong person found out about it so he tried to destroy it. Unfortunately, he found no way to destroy it so he instead put a barrier around it and buried it in a konpaku to try and conceal its location.
It All Comes Together
The konpaku Urahara decided to conceal the Hou Gyoku was Kuchiki Rukia. Urahara, finding Rukia after she gave her shinigami powers to Ichigo, offered her one of his gigai. The gigai just happens to be one of the special ones that eats her remaining powers. It seems that Urahara is trying to hide Rukia from Soul Society's detection since she is the carrier of his dangerous creation.