From Wiki

Father of Chani Kynes. Son of Pardot Kynes.

Liet was the imperial ecologist on Arrakis after the death of his father. He was also the judges of the change when House Atreides took over control of Arrakis.

Apart from being in the service of the emperor he was also (and more importantly) the leader of the Fremen when House Atreides took control of Arrakis. In this capacity he saved the lives of Paul Atreides and his mother Jessica.

Liet died in the desert due to the Baron Vladimir Harkonnen.