who was the leader of zanj rebelion and what was his nationality

The leader of the Zanj Rebellion was Ali ibn Muhammad , and he is generally described by historians as Arab , likely of Arab origin.

Quick context

The Zanj Rebellion ran from 869 to 883 in southern Iraq and was led by Ali ibn Muhammad, who rallied enslaved East African workers and other discontented groups against the Abbasid Caliphate.

Nationality

His nationality is usually given more as Arab than by a modern nation- state label, since that period did not use modern nationalities in the current sense.

Extra note

Some sources mention he came from near Ray in present-day Iran, but still describe him as Arab or of Arab descent.