A.T. Robertson Commentary Galatians 5:10

"I have confidence to you-ward in the Lord, that ye will be none otherwise minded: but he that troubleth you shall bear his judgment, whosoever he be." — Galatians 5:10 (ASV)

Whosoever he be (οστις εαν η). Indefinite relative clause with εαν and subjunctive. It seems unlikely that Paul knew precisely who the leader was. In 1:6 he uses the plural of the same verb ταρασσω and see also αναστατουντες in verse 12.