Behind Jesus stands Hillel. Hillel is one of the most important figures in jewish spirituality, and is considered the founder of the rabbinic tradition - the first rabbi - although he was never called that during his lifetime. The words of Jesus in the gospel clearly echo the words and philosophy of Rabbi Hillel.
Now, what do I mean by the foundation of the rabbinic tradition? Weren't there always rabbis? Keep in mind that in Jesus' time there were still jewish priests, who, besides being the spiritual leaders of the jewish community, also performed the sacrifices in the Temple of Solomon in Jerusalem. Yes, animal sacrifice as well as offerings of fruits and other foods, and incense, were a daily practice in judaism before the romans destroyed the Temple of Solomon in 70 AD. Of course, in the first century these practices were univeral all over the world - not to sacrifice would have been strange, and it was one of the things that distinguished the early christians. The christian tradition that grew up after Jesus' death, that his death on the cross was a sacrifice, as the lamb of god, to atone for the sins of all men, is directly related to the jewish practice of literal sacrifices of spotless lambs to atone for sins at the Temple of Solomon.
Since there was only one temple, in Jerusalem, houses of study had sprung up in the jewish communities, which were often called by the greek term, synagogue. These were places where jews gathered for prayer and studies, just like their modern counterparts. Naturally, some became teachers of others, eventually being called Rabbis (literally 'master', but as the term usually used to address teachers - hence, to call someone a rabbi is to address them as your teacher). Rabbis, however, always supported themselves at some other trade until three or four centuries after Jesus. Hillel is supposed to have been a woodcutter.
Hillel, a poor boy from babylonia, grew up to become the most revered sage of his age. He is thought to have been the head of the community of jewish teachers from about 30BCE to his death about 10CE. Hillel was noted for his extreme mildness, and the school of thought that he founded took the forgiving view of the law which prevails today in judaism, in opposition to his peer Shammai, the irascible engineer, whose school took a more severe view.
The two sages figure in the most famous and telling anecdote about Hillel. It seems a foreign potentate approached Shammai, saying that he would convert to judaism if the teacher could explain it to him while standing on one foot. Shammai threw him out of his office. The potentate then approached Hillel with the same proposition. Hillel said "What you would not want done to you, do not do unto others. This is the whole of the Law and the Prophets - the rest is commentary. Go and study."
When Jesus enunciates his version of the golden rule, it would have been clear to those listening to him that he was affirming his membership in the school of Hillel. (Some people make much of the difference between the negative form that Hillel used and the positive form that Jesus used, but from my point of view this is splitting hairs.) Jesus would have been saying this only twenty years after Hillel's death, and by declaring himself a pharasee (more about this later) of the school of Hillel, Jesus would have been making a declaration of where he stood in the philosophically fractured and contentious jewish society of his time.
Other famous sayings and traditions of Hillel show similarities to Jesus and the things that he said. Hillel's famous mildness sets the tone that Jesus so clearly follows - there is a story that some friends of Hillel's made a bet that they could make Hillel lose his temper. Although they made rude remarks about his being from babylonia and were generally obnoxious, they lost the bet. In the Pirkei Avot, Hillel is quoted as saying (in regard to showing pride of learning) "One who advances his name, destroys his name ... And one who make personal use of the crown of Torah shall perish." Another saying of Hillel reads, in part "Do not judge your fellow until you have stood in his place". Also, "Because you drowned others, you were drowned; and those who drowned you, will themselves be drowned." And finally "One who increases flesh, increases worms; one who increases possessions, increases worry ... one who increases charity, increases peace."
To Jesus' listeners, his standing in the tradition of Hillel would have been so obvious as to go without saying.