Imam ‘Ali (a.s.) said:
لِلظّالِمِ ثلاثُ عَلامات: يَظْلِمُ مَنَ فَوْقَهُ بِالْمَعْصِيَةِ وَ مَنْ دُوْنَهُ بِالْغَلَبَةِ، وَ يُظاهِرُ الْقَوْمَ الظَّلَمَةِ
The oppressor has three signs: oppresses those who are higher than him through opposition and disobedience, and oppresses those who are inferior to him through violence and predominance, and cooperates with other oppressors.1
When the ugly urge to oppress becomes ingrained and dominates one’s mind, it shows up in different ways depending on the situation. If he cannot oppress overtly a strong opponent, the oppression takes subtle forms like disobedience and dereliction of duties. Against the weak, the oppressor resorts to open aggression, force, violence and injustice . Another sign of an oppressor is that he selects his friends and companions from among the unjust.