Born as an experiment from the Hidden Sand Village, Gaara was combined with the spirit of a demonic sand priest known as Shukaku, not unlike Naruto and the Nine Tails. Gaara grew up without knowing love. For a long time he thought being spoiled equals love, but when he met Rock Lee that opinion changed. Unfortunately, Gaara became unstable around the age of six years. Consequently, his father Kazakage, ordered numerous assassination attempts upon him, all failing miserably. This betrayal caused Gaara to become hateful and deeply suspicious of everyone, including his siblings, who he regarded as "lumps of meat linked together by hatred and murderous intent."
The tattoo on Gaara's forehead means love, which combined with his name means, "I Love Death". Since he only feels alive when he kills, he believes that killing is his reason for being. The tattoo was put on Gaara's head by Gaara himself after his abilities killed Yashamaru. Yashamaru, being the one that raised Gaara, and the only one that seemed to care for him.
Although Gaara's father asked Yashamaru to kill Gaara, Yashamaru says he had willingly accepted the mission. Having never truly loved Gaara, hoping that killing him would avenge the death of his sister. Yashamaru eventually detonates himself with explosive tags covering his body, with his last words being "please die". Gaara survived the blast without even being injured, losing the only person he thought cared for him, losing his fate in bonds and love.
When we take a look at Naruto Shippuuden we notice Gaara has undergone some personality changes. His relationship to his siblings has become somewhat normal. He has come to consider Kankuro and Temari as his brother and sister where he used to threaten to kill them if they got in his way. He talks to Kankuro about his problems and dreams.
In a conversation Gaara has with Kankuro, Gaara says: "In order to escape a path of loneliness, I have no choice to but to work hard and make my own path. If I do that, then someday... someday I can be like him. That's why as a shinobi of the Sand I'll aim to be the Kazekage. So I can live a life connected to my village. I want to work hard so that other will accept my existence." It's obvious that Naruto inspired Gaara to question his bonds with other people. Suffering, sadness and joy - He want to be able to share it with another person, he want his existence to be necessary to other people, not as a weapon to be feared but as the Hidden Sand's Kazekage. He eventually follows up his dad as the Fifth Kazekage and really acts as the villager's protector as seen in his fight with Deidara. The villagers also have come to respect Gaara, and the younger females of the village even like Gaara. In the beginning of Shippuuden Gaara fulfills his role as the village's Kazekage, but gets taken by Akatsuki doing so. Gaara apparently dies from having Shukaku extracted from him by Akatsuki, and later on Chiyo sacrifices herself to bring him back to life.