The Order of the Phoenix
The original Order of the Phoenix was founded by Albus Dumbledore with the purpose of fighting Voldemort. Its members included the Potters among many others. The following are the members who have had the most interaction with Harry.
As time has passed on in Harry's life, the headmaster of Hogwarts has become more then just a school administrator. It was Dumbledore who was responsible for placing Harry in a safe location after the murder of his parents. Harry truly looks up to Dumbledore, and often remarks that he thinks Dumbledore is the greatest wizard, at least of his time. However, after Sirius' death, it seems that some of Harry's adoration for Dumbledore had decreased and been replaced with anger. Dumbledore didn't tell Harry until his fifth year of the prophecy that has been the cause of so much suffering in Harry's life. He didn't help Harry with his occlumency lessons, either. Had Harry been properly taught, it may have saved Sirius' life.
After weeks of little to do but think of what had happened, Harry seemed welcome to trusting Dumbledore again. To Harry's surprise, Dumbledore began explaining a great deal of things to Harry regarding Voldemort. Together, they went after one of Voldemort's Horcruxes. Upon their return to Hogwarts from their mission, Dumbledore was murdered by Snape. With the last year of guidance Dumbledore was able to give, Harry now had the tools he needed to defeat Voldemort.
However, Harry could never have anticipated how his feelings towards Dumbledore would change once again. He began to doubt Dumbledore was again as he learned rumors and half-truths about Dumbledore's own family and his association with the dark wizard Grindelwald. When Harry viewed the memories that Snape gave him just before he died, he learned that Dumbledore knew the tragic truth of Harry's fate all along. Dumbledore knew that Harry was indeed a Horcrux and would have to die at Voldemort's hands in order to allow for Voldemort to become mortal again. Harry felt this was another betrayal, but he continued on his path and sacrificed himself.
After Voldemort attempted to kill Harry, Dumbledore guided Harry one last time. He explained that like Grindelwald, he had been obsessed with the Deathly Hallows. He wanted to bring his own parents back so that they could care for his magically unstable sister, Ariana. But he also wanted the power the Deathly Hallows would bring. His experiences taught him that he was not trustworthy with power, and had to content himself being a teacher instead. Finally, Dumbledore told Harry that he was at last truly free, and the piece of soul left in Harry was now gone forever.
Although Harry had unknowingly met other magical people during the first ten years of his life, the first he really got to know was Rubeus Hagrid, gamekeeper of Hogwarts. Under Dumbledore's orders, Hagrid was the one who took Harry to Privet Drive. It was also Hagrid who introduced Harry to the magical world. Hagrid took Harry to Diagon Alley to help him shop for his first year at Hogwarts. And throughout Harry's years at Hogwarts, Hagrid has always been a friend to Harry.
After Dumbledore's death, Hagrid evidently took to living near Hogwarts with his brother Grawp. Both participated in the battle at Hogwarts, and Hagrid was taken prisoner by the Death Eaters at one point. After Voldemort attempted to kill Harry, Hagrid was charged with carrying his body to show the fighters at Hogwarts.
After Voldemort's defeat, Hagrid evidently went back to being Gamekeeper for Hogwarts.
When Remus was at Hogwarts, he was one fourth of the group that called themselves the Marauders. This group included Sirius Black, Peter Pettigrew and James Potter. Remus became the Defense Against the Dark Arts teacher
at Hogwarts during Harry's third year. According to Harry and others, Lupin was the best teacher they ever had. With Lupin's help, Harry learned how to master the Patronus Charm which gave him a defense against the Dementors. Even more importantly, Harry learned that year the truth about who had betrayed his parents. Lupin was forced to leave Hogwarts when it was leaked that he was actually a werewolf. After Voldemort's return, Lupin along with others, worked to revive the Order of the Phoenix. In Harry's sixth year, Lupin infiltrated the werewolves to gain more information about Voldemort's activities.
In the summer after Harry's sixth year, Lupin and Tonks were married in a quiet ceremony. Lupin eventually met up with the trio at Grimmauld Place and offered his help to them. When Harry learned that he had left Tonks, who was pregnant, at her parents house, he became angry and insisted that Lupin should stay with his family. Lupin left in a hurry, and Harry immediately felt terrible for what he had said. However, this conversation seemed to be a mere memory by the time Harry saw Lupin again. Lupin insisted that Harry be godfather to his new son, Teddy.
Sadly, both Lupin and Tonks were killed by Death Eaters during the final battle at Hogwarts. However, unlike the pathetic life Harry lived as an orphan, it appears Teddy has been well cared for by his grandmother, godfather, and other friends of his parents.
Nymphadora Tonks Lupin
Nymphadora (or Tonks as she preferred to be known) first met Harry as part of his guard to get him from the Dursleys to Grimmauld Place. She also took part in the Department of Mysteries battle at the end of Harry's fifth year. During Harry's sixth year, she fulfilled various duties in protecting Hogwarts and saw Harry on occasion. She noticed he was missing after the Hogwarts Express arrived at Hogsmeade and rescued him from the hex Draco Malfoy had put on him. Tonks was present, along with her husband Lupin, at the final battle and was killed by Bellatrix. Lupin was killed by Dolohov, which left their son an orphan.
McGonagall is the head of house for Gryffindor, therefore Harry has interacted with her many times. It is she who witnessed Harry's flying abilities and immediately invited him to join Gryffindor's Quidditch team during his first year. She also was quite adamant about Harry becoming an Auror, telling the infamous Dolores Umbridge that she would personally do whatever she could to help Harry achieve that goal. McGonagall helped organize the teachers and students when Voldemort and the Death Eaters were preparing to strike. She helped Harry get the time he needed to search for Horcrux hidden in Hogwarts.
Severus Snape was once a lonely child who came from a difficult background. But he was friends with a clever witch named Lily Evans. This relationship would shape his life forever, even long after Lily's death.
He was the one who overheard part of the prophecy given Dumbledore regarding "the one with the power to vanquish the Dark Lord." When he learned Voldemort intended to go after the Potter's, Severus tried to save the them, and more importantly to him, Lily. He told Dumbledore what was going to happen, and agreed to become a spy. Due to Pettigrew's treachery, James and Lily were killed anyway.
But Severus stuck to his promise, and told Dumbledore he would help him in any way possible when it came to protecting Harry. He was even outraged when Dumbledore revealed to him that Harry would have to die. No matter what, Harry was still Lily's son to Severus, even though he never truly liked Harry at all. When the time came, he assisted Harry in his journey for the Horcruxes by passing the sword of Gryffindor to him at the proper time. Snape was murdered by Nagini, but not before passing on his memories of Lily to Harry. More importantly, these memories showed Dumbledore explaining to Snape (and to Harry) that Harry must be killed by Voldemort in order for the Horcrux inside Harry to be destroyed.
With this new knowledge, Harry probably cleared Snape's name after Voldemort's defeat. Harry even named his second son Albus Severus, and told his son that Severus was one of the bravest men he had ever known.