Count Hasimir Fenring was raised in the imperial court and befriended the prince who later became the Emperor Shaddam IV, with a little help from the count and some poison.
Count Fenring is a failed part of the Bene Geserit breeding scheme to produce a super being, hoverer he was born a eunuch, unable to breed. Hasmir was however supremely skilled in many areas, but chose to become chief assasin to house corrino. He married a bene geserit sister, which guaranteed his loyalty to the sisterhood even over that of his life long friend the Emperor.
The Fenrings, in keeping with court secrecy have their own secret language (probably a variation of a bene geserit code), that sounds much like humming to those not in the know, this make them seem bumbling and harmless.
The Fenrings kept a grand house on Arrakis in the city of Arrakeen, during the Harkonnen rule there. Fenring's house was later used as the home for the royal family of House Attriedes, under duke Leto's rule. After Leto's son, Paul seized control of Arrakis and the empire Frening was ordered by Shaddam to kill Paul. Although apparently capable Fenring refused, not wishing to kill the bene geserits long sought after super being.