spin doctor

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Slang A person who publicizes favorable interpretations of the words and actions of a public figure, especially a politican.

Wiktionary

1. n. A person employed to gloss over a poor public image (or present it in a better light) in business and politics, especially after unfavourable results have been achieved. A lobbyist; PR person.
2. v. To generate spin (favourable interpretation or bias).

GNU Webster's 1913

1. n. a spokesperson for a political party or candidate who tries to forestall negative publicity.

WordNet 3.0

1. n. a public relations person who tries to forestall negative publicity by publicizing a favorable interpretation of the words or actions of a company or political party or famous person