Zacchaeus was a chief tax collector in Jericho who, according to Luke 19, climbed a sycamore tree to see Jesus and afterwards received him into his house.
Luke 19:2-4 in the King James Version reads:
2 And, behold, there was a man named Zacchaeus, which was the chief among the publicans, and he was rich. 3 And he sought to see Jesus who he was; and could not for the press, because he was little of stature. 4 And he ran before, and climbed up into a sycomore tree to see him: for he was to pass that way.
These verses open the account of Zacchaeus in Luke 19. Read it in context at Luke 19:2-4, or the full chapter at Luke 19. Encyclopedia entry: en.wikipedia.org/wiki/Zacchaeus.