The importance of the Gracchi brothers (Tiberius and Gaius) in Roman history cannot be overestimated. Most scholars would say that the actions of the Gracchi brothers was one of the most important events in Roman history.
They are important for two reasons. First, Tiberius saw that one of the great problems of Rome was debt and poverty of the free population. He saw that the wealthier were simply getting more than their fair share and the poor were being pushed off the land. So, he wanted to redistribute land. So, when he took office as a Tribune of the Plebs in 133 B.C., he began to to introduce his land reforms. He pass a law called, Lex Sempronia Agraria, which basically stated no one could own more than 500 iugera of public land, that is, land taken in the course of warfare. With this extra land, he wanted to redistribute it to the poor.
Tiberius' actions were not completely novel, because there was a law on record (Licinian laws), which stated the limitation of land to 500 iugera. However, it was not enforced.
As anyone could imagine, the wealthy did not want to give up their lands. Some built farms on them and others their country villas. The situation was complicated, to say the least.
Second, the way the Gracchi brothers went about passing their land reforms was new. What usually took place was all laws went to the senate first and then to the concilium plebis (council of the people) for voting, but the Gracchi knowing that the senate would never agree bypassed the senate and went directly to the concilium plebis. This angered the elite very much. There was even talk of Tiberius aiming for tyranny through popular support.
Tiberius was clubbed to death in 133 B.C. His brother, who followed his brother's policies, was killed ten years later.