How can I relate to an object twice in rails?

Question

I've got a Users model and a Tasks model.

A task has a creator, of type user, and an assignee of type user.

I've already done a migration of AddUserIdtoTasks to get the creator relation working, but now I need to do the same thing again to add the assignee, but I'm already using the keyword 'user'. How should I go about building a proper relation.

A task only has one assignee, always.

I'm using devise for the user model.