Conversation so far:
What is the corporation?
The Rock allied with Vince and Shane McMahon as the crown jewel of their stable, The Corporation.
What can you tell me about the corporation?
beginning a feud with Triple H, The Undertaker and The Corporate Ministry that saw The Rock defeating Triple H.
what did they do in the corporation?
The Rock, who then lost the title rematch at Backlash: In Your House and was thus betrayed by Shane McMahon.

Question: When did he join the corporation?
Self-contained rewrite: When did The Rock join the corporation?