What is the relationship between 'Boko Haram' and 'Abubakar Shekau' in the context of the input sentence.
Options: legal form, distribution format, chairperson, creator

Leader of the Boko Haram sect, Abubakar Shekau has again resurfaced in a recording and denied claims by Chadian … see more » Copyright © 2015 Vanguard.
chairperson