This is the 4632nd most frequent Turkish word.
biriydi
"Biriydi" means "he/she/it was someone" in English.
'Biriydi' is used to express a relationship between the subject (the person) and the set of well-known doctors in the city.
O, şehrin tanınan doktorlarından biriydi.
He was one of the well-known doctors in the city.
In this context, 'biriydi' is used to indicate membership in a group, specifically referring to Ahmet being one among the most hardworking students.
Ahmet okulun en çalışkan öğrencilerinden biriydi.
Ahmet was one of the most hardworking students in the school.
Here, 'biriydi' denotes a single instance within a collection or category of interesting experiences.