The Second Caliph - Umar Al Farooq

The Prophet saw said, “Among the nations that came before you were men who were inspired with guidance even though they were not prophet such people were to exist from my followers it would be Umar ra. (Sahih Bukhari)

When Umar ra became a Muslim he wanted everyone to know that he had left falsehood, for the truth. This is why he was known as Al Farooq (The Distinguished between truth and falsehood)