Of all the characters in Naruto, Iruka Umino is one of the most important. He was Naruto's teacher before Kakashi, and he watched Naruto grow up into the troublemaker he would become as a way to get attention. He watched the other villagers turn their backs on a child who lost his parents and never understood why he was so hated. He was also the one that would always be there for Naruto.
Unlike the other villagers, Iruka understood that Naruto didn't ask for the Fox Spirit to be sealed away in his body. He understood that Naruto didn't even know that he was a vessel for this dangerous spirit. As his teacher, it was his responsibility to make sure Naruto could become the best ninja he could. He even acted as a mentor to Naruto outside of the classroom, all because he knew what it was like to be in the young orphan's shoes.
Iruka's parents were killed in the Nine-Tailed Demon Fox's attack on the village. As a result, he became a troublemaker, hoping it would get him the attention he craved and needed. The Third Hokage would cheer Iruka up when he was at his lowest, but others would be nice to him as a farce to get in the Hokage's good graces. Watching Naruto fall into the same trap, he knew that he needed to be the person in Naruto's life that Iruka never had. It wasn't until he stole the Scroll of Seals and was attacked by Mizuki that Naruto realized just how much Iruka believed in and cared for him.
Iruka saved Naruto from becoming like Gaara just by being there for him. Gaara was isolated for most of his life, being the vessel for the One-Tailed Shukaku. Much like Naruto, he was feared by the other villagers, and when he was allowed to walk around the village, he would end up hurting or killing others with his sand because he couldn't control his powers. This only made things worse for Gaara, as he couldn't find anyone to make an emotional connection to. He didn't even understand the concept of pain due to his sand protecting him. The only person he had in his life that he thought cared for him was his maternal uncle Yashamaru, but even he would go on to try and kill Gaara by command of Gaara's father. After this assassination attempt, Gaara would vow to live only for himself, leading him to become an emotionless killer.
Naruto could have become just like Gaara had Iruka not been there. Gaara lacked someone who genuinely cared for him and tried to be a friend and mentor. Iruka was there for Naruto, becoming the support that someone like Naruto and Gaara needed. Luckily for everyone, even Gaara, Iruka was there for Naruto.
By being there for Naruto, he was able to help not only Naruto but Gaara and many others by extension. Naruto taught Gaara that living for others could be fulfilling, and once Gaara started living for others, he became a happier person. He even went on to become Kazekage of his village. Iruka not only saved Naruto, he saved Gaara and everyone else Naruto helped using the empathy he learned from him.