2 definitions:

assignee
Definition:

Individual to whom a title, claim, property, interest, or right has been transferred.
http://www.investorwords.com/294/assignee.html


as·sign·ee

1. A party to which a transfer of property, rights, or interest is made.
2. One appointed to act for another; a deputy or agent.
http://www.thefreedictionary.com/assignee

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Note added at 16 mins (2008-05-30 13:21:41 GMT)
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Alternatively government agent:
Definition of government agent
A representative or official of a government or administrative department of a government
agent - a representative who acts on behalf of other persons or organizations
FBI agent, G-man, government man - a special law-enforcement agent of the Federal Bureau of Investigation
revenuer - a government agent responsible for collecting revenue (especially one responsible for stopping bootlegging)
T-man - a special law-enforcement agent of the United States Treasury
http://www.thefreedictionary.com/government agent