Qareen
What is a Qareen? A shaytaan, a devil, assigned to someone to mislead and misguide him. Someone to whisper to him in the light of day and the darkness of night. Allah says:
وَمَن يَعْشُ عَن ذِكْرِ الرَّحْمَنِ نُقَيِّضْ لَهُ شَيْطَاناً فَهُوَ لَهُ قَرِينٌ Translation: And whoever is blinded from remembrance of Ar-Rahman, we appoint for him a qareen, and he is to him a companion. [Surah Az-Zukhruf, verse 36]