Conversation so far:
What is The W?
The group reconvened once again to make The W, though without Ol' Dirty Bastard, who was at the time incarcerated in California.
Was this a success?
The W was mostly well received by critics.
Did it win any awards?
The album would go on to reach double platinum status.
What is Iron Flag?
In 2001, the Wu-Tang Clan released Iron Flag, an album which made extensive use of outside producers and guests.

Question: Who did they collaborate with?
Self-contained rewrite: Who did Wu-Tang Clan collaborate with on the album Iron Flag?