I was told that Abu Zar Ghifaari was extremely harsh.

Answer

Hadhrat Abu Zar Ghifaari (rahmatullah alayh) was a very senior Sahaabi of Rasulullah (sallallahu alayhi wasallam). People should restrain their tongues when they desire to speak deprecatingly of Rasulullah's Sahaabah. What we know about Hadhrat Abur Zar (radhiyallahu anhu) is that Rasulullah (sallallahu alayhi wasallam) said that Allah Ta'ala had instructed him to love (specifically) four Sahaabah. One of the four is Hadhrat Abu Zar Ghifaari (radhiyallahu anhu). Also mentioned in the same Hadith is that Allah Ta'ala loves these four.