Although he certainly made good use of them, Jesus didn't invent the parable. They can be found throughout the Old Testament, and are still in use today, especially in the eastern world, but even in this country we often use similar methods of teaching, although we sometimes think of them as illustrations, analogies, and metaphors.
One of the earliest parables in the Scriptural record is that of Jotham, in which the trees are represented as seeking to anoint a king to rule over them (Judges 9:8). Another Old Testament parable is that of Jehoash, where a thistle is described as seeking an arranged marriage with a cedar (2 Kings 14:9).
When Christ used parables as means of reaching his audience, it would have come as no surprise to them. They were expected, even prophesied.
I will open my mouth in parables, I will utter things hidden from of old - things we have heard and known, things our fathers have told us. -- Psalms 78:2-3
Jesus, and many of those who he was speaking to, were well aware of this. When asked by his disciples why he spoke to the people in parables, he replied:
The knowledge of the secrets of the kingdom of heaven has been given to you, but not to them. Whoever has will be given more, and he will have an abundance. Whoever does not have, even what he has will be taken from him. This is why I speak in parables:
Though seeing, they do not see;
though hearing, they do not hear or understand.
In them is fulfilled the prophesy of Isaiah ... -- Matthew 13:13-14
Jesus spoke all these things to the crowd in parables; he did not say anything to them without using a parable. So was fulfilled what was spoken through the prophet:
"I will open my mouth in parables,
I will utter things hidden since the
creation of the world." -- Matthew 13:35
Christ's ministry didn't extend much beyond three years, so we can surmise that the central themes and topics of his messages were recorded for us by the authors of the New Testament, albeit in condensed form, and a large percentage of his teaching was in parables.