Rasa

The was the previous leader of Sunagakure. He is the father of Temari, Kankuro, and Gaara, and husband of Karura. His actual name is currently unknown.

Background
By his order's, the One-Tailed Shukaku was sealed within Gaara so that he could become Suna's ultimate weapon. However, as Gaara grew and his abilities began to manifest, the Fourth realized that this had been a poor choice and started to view Gaara as a failed experiment who was a threat to the inhabitants of Suna. In time, the Fourth began issuing orders for Gaara's assassination, none of which were ever successful. After a while, for reasons unknown, the Fourth stopped issuing attempts on his son's life.

Invasion of Konoha
The Fourth was also the one to join with Orochimaru in his attack on Konohagakure, hoping to teach the daimyo a lesson and to re-establish the Suna's military force. Things, however, did not go as planned for him; just before the Chunin exam's third stage, where his attack was planned to take place, he was betrayed and impaled by his ally, Orochimaru, who stole his identity.

Ironically, the son whose life he made miserable, Gaara, became the new Kazekage in his place.

The Fourth Kazekage was seen once more in flashback of Kimimaro where Orochimaru was seen impaling him through his heart, thus killing him, though this flashback only appears in the anime. Kabuto Yakushi and Kimimaro were also at the site.

Abilities
His level of strength is not shown but given he was selected to be the Kazekage, it can be assumed he possessed some power. However, considering how easily Orochimaru defeated him, it's presumed he was fairly weak (though at that time, Orochimaru was very powerful, capable of besting the Hiruzen Sarutobi, the Third Hokage). Also, in the anime only, it's shown that Kimimaro assisted with the Fourth's death, so it's also possible that the Fourth was powerful but in the end he was overwhelmed by Kimimaro and Orochimaru's power. All in all, the full extent of his power is unknown.