Danzo Shimura, known as the Darkness of the Shinobi, was often seen as the darkness to Hiruzen Sarutobi's light. He was the antiheroic shinobi from the Shimura clan, and an elder of Konohagakure. He was the leader of the disbanded ANBU faction, Root (the infamous group that did all the dirty work the Third Hokage did not "feel capable of doing.").
In his childhood, Danzo was said to be Hiruze Sarutobi's best friend and rival. The rivalry, however, seems to be have been more one sided, as Danzo was never able to keep up with Hiruze. It was said that at some point during the First Shinobi World War, Danzo was on a mission with Tobirama's (the second Hokage) team when they were surrounded by elite shinobi (Kinkaku squad) from Kumogakure. At this time, while he wanted to volunteer to be the decoy and face certain death, his fear of death prevented him from doing so. Eventually Hiruzen volunteered, but Tobirama ultimately concluded he would stay to be the sacrifice.
Danzo then grew up trying to scheme a way to become the next Hokage. He was allowed by the Third to create the Root Faction of the ANBU force, which carried out Danzo's will in the name of Konoha. Eventually the force was disbanded, but carried on secretly. Danzo often recruited young shinobi into the force at a very young age, brainwashed them to never feel or question his command, and do as instructed.
Danzo eventually was nominated to be the 6th Hokage, after the invasion of Pain left Tsunade in a coma. He attended the meeting of the 5 Kage as Konoha's representative. While there he was exposed for trying to manipulate Mifune, the meeting's impartial moderator, to give him control of the alliance's army. Disgraced, he left and on his way back, he and his bodyguards were confronted by Sasuke and Tobi.
It was at this stage that Sasuke finally took revenge for his brother, Itachi. Sasuke finished Danzo off, but not before Danzo tried to kill Sasuke, Tobi, and himself with one final attack.
Danzo was clearly very devoted to Konoha. While he believed he wanted nothing but the best for the village, I do not believe he ever would have done that did not first protected himself. This was most notable when he failed to sacrifice himself for his friends due to his fear of death.
Personally I just think he wanted power, and would have done anything to get it. What do you think?