ANSWER: Jesus, in this well-known good Samaritan parable, used a group of despised people to illustrate that love and mercy triumphs over biases, hatred and alike. It is interesting to note, in this particular story, that the Lord never actually uses the term "good Samaritan," although that is certainly implied (Luke 10:29 - 37).
It is also interesting to note that during his ministry Jesus told at least seventy stories meant to highlight a particular lesson or spiritual principle. The one we label the Good Samaritan parable is found only in the book of Luke. His gospel contains twenty-one of these kinds of illustrations, with this particular story being the second one he records.
Generally, a Samaritan would be an inhabitant of either the city or region of ancient Samaria. The city itself was purchased by Omri, the sixth king of Israel (885 - 874 B.C.) and named after its former owner. Over time the entire northern kingdom of Israel was also called Samaria (1Kings 13:32, Jeremiah 31:5). After a three-year assault by Assyrian kings beginning with Shalmaneser V, the city fell to his army in 723 B.C. (2Kings 17:6, 18:9 - 12). Thousands of people were deported to Assyria while Assyrians migrated to the area. From this point onward, a Samaritan was consider "mixed" since those new in the land intermarried with the poorest Israelites that were left by the Assyrians.
The marriages between the remaining Israelites in the land and Assyrian Gentiles led to the widespread worship of pagan gods. This was the beginning of the animosity between an average Samaritan and the Jews. Later in history, a man named Manasseh, of a priestly lineage, obtained permission from Persian King Darius Nothus to build a temple on Mount Gerazim for those in Samaria because they had given him refuge. This enraged the Jews even further.
The animosity felt by Jews in Judea toward these people continued up to the time of Christ (Luke 9:53 - 54; 10:25 - 37; 17:11 - 19; John 8:48), which is why he used them in his parable to make a point. Their hatred was so great that when they traveled from Galilee to Judea they would bypass Samaria through the barrenness of Petra just to avoid contact. Jesus, however, rebuked His disciples for being hostile toward these people (Luke 9:54 - 56).
Christ, of course, loved these people as much as anyone else. Luke 17 gives the account of him healing a Samaritan leper and praising him for being grateful. He also honored a person from Samaria for being neighborly (Luke 10:30 - 37), asked a woman from the area for a drink (John 4:7), and preached directly to them during his ministry (John 4:40 - 42). This information should hopefully help your understanding of this fascinating story.