These are the members of Voldemort's army that have had the most contact with Harry.
Barty Crouch Jr.
Barty Crouch Jr. was one of the more devoted Death Eaters. He, along with Bellatrix and others, tortured the Longbottoms in an effort to locate Voldemort. Years later, Voldemort used him to get at Harry Potter. Through the use of the Polyjuice Potion, Barty became Mad Eye Moody who was to be the Defense Against the Darks Arts teacher in Harry's fourth year. Barty entered Harry into the Triwizard Tournament and helped him get through the three tasks. Just as Barty had planned, Harry was delivered to Voldemort which allowed for Voldemort's revival. The truth was uncovered, but Barty was silenced by the Dementor's Kiss.
Bellatrix Lestrange is one of Voldemort's best warriors and certainly his cruelest. She murdered her cousin, Sirius Black (Harry's godfather) in the Department of Mysteries battle in Harry's fifth year. Harry chased after her and attempted for the first time to use an Unforgivable Curse. It barely did anything to her and she proceeded to inform him that he needed to really mean it for it to work.
Harry once again saw Bellatrix when the trio was captured by Snatchers and taken to Malfoy Manor. When Bellatrix saw they had the sword of Gryffindor with them, she panicked and gave away a crucial clue. Harry deduced that she might actually have another Horcrux in her possession. The trio broke into the Lestrange's vault at Gringotts and were rewarded with Hufflepuff's Cup, the one Horcrux Voldemort had entrusted to Bellatrix.
Bellatrix met her end in the final battle as she was defeated by Molly Weasley.
Draco is pureblood wizard and the son of Narcissa and Lucius Malfoy. Harry and Draco first met in Madame Malkin's robe shop. It was there that Draco first began to make an enemy of Harry for he insulted Hagrid, Harry's only friend at the time. On the first day at Hogwarts, Draco offered his friendship to Harry once he learned who he was. He told Harry he could help him stay in the "right" crowd. Harry rejected this offer, preferring to stick with Ron Weasley, and later Hermione Granger. It is Draco's intolerance of other students that made him an enemy of Harry and many other students. Draco insulted the Weasleys (for being poor) and Hermione (for being muggle-born) at any chance he got.
Draco Malfoy was once little more then an ignorant school-yard bully. During Harry's sixth year, this changed. After his father was caught and sent to Azkaban, Voldemort called on Draco to perform a special mission. This mission was to kill Albus Dumbledore. Draco's mother, in pure fright, approached Snape and asked him to help her son. During the school year, Draco tried weakly several times to accomplish his mission. All along, Harry was a step or two behind him, trying to figure out what he was up. Draco finally got his chance on the Astronomy Tower as Dumbledore and Harry were returning from their own mission. Draco could not finish the job he was given, and instead it fell upon Snape to kill Dumbledore.
Draco and Snape apparently returned to Voldemort's side after Dumbledore's death. Like other purebloods, Draco returned to Hogwarts for his seventh year while Voldemort and his Death Eaters took up residence at Malfoy Manor. Draco and Harry met once again when the trio were captured and brought to face Voldemort. In the ensuing madness, Harry overpowered Draco and took his wand. They once again met on the night of the final battle, as Harry and the others saved Draco's life not once, but twice. However, the favor was returned when Narcissa risked herself by lying to Voldemort when telling him that Harry was dead.
The final time interaction known between Harry and Draco occurs nineteen years later, as both fathers say goodbye to their own children at King's Cross. A look and nod is all that is shared between them. One can assume that everything Draco went through greatly affected him, and he would not be the same person he once was.
Lucius, Draco's father, is one of the more slippery Death Eaters. He escaped any kind of prison sentence because he had supposedly reformed. In Harry's second year of Hogwarts, Lucius slipped a dangerous diary into Ginny Weasley's cauldron. This diary was in fact a Horcrux, something Lucius clearly didn't know. Like most former Death Eaters, Lucius returned Voldemort after his revival. Lucius was in charge of the mission to get the prophecy in the Department of Mysteries. That mission failed badly, and Lucius found himself in Azkaban at last. However, he wasn't there for much longer then a year. He, his wife Narcissa and Draco were the unhappy hosts of Voldemort and the other Death Eaters at their home: Malfoy Manor.
Thanks to Narcissa saving Harry's life near the end of the final battle, the Malfoys once again escaped punishment.
Peter Pettigrew was once a part of a close knit group of friends that included Harry's father. When the Potters went into hiding, Peter became their secret-keeper. Voldemort hardly needed to purse Peter for information as he was already a spy for Voldemort. He gave up the Potters location which allowed Voldemort to find them and kill Harry's parents. Pettigrew changed into his animagus form (a rat) and stayed with the Weasleys after Voldemort's supposed defeat.
The truth of Pettigew's loyalty came out in Harry's third year when Sirius escaped from prison and sought his revenge against Peter. Sirius had been sent to Azkaban for killing muggles and many believed he had been the one to betray the Potters. However, Harry chose to save Peter's life This debt was finally settled in the basement of Malfoy Manor when Pettigrew hesitated for a mere moment in handing over Harry. His silver hand, a gift from Voldemort, strangled him because he was not faithful in that one tiny moment, but it was enough to help Harry and his friends escape.