A demonstrative (ism al-ishārah) presents an identifiable person or object as if pointing toward it. “هَذَا” (this) does not merely name a person; it directs the hearer’s attention to an indicated subject.
هَذَا أَبُو الصَّقْرِ فَرْدًا فِي مَحَاسِنِهِ
This is Abū al-Ṣaqr, singular in his fine qualities.
The expression first singles the person out, then attributes distinctive merits. When physical or mental pointing is available, this can be more vivid than supplying only a proper name. The surrounding context may add admiration or surprise.