Actress, writer and occasional singer of the 'Mad Men' theme, Allison Williams is our Crush of the Day. Aside from being stunningly beautiful and talented, 2010 Yale grad Williams is incredibly smart.

The daughter of highly regarded NBC news journalist Brian Williams, Allison Williams, 23, is one of the stars of 'Girls,' the HBO show about 20-something aged women that makes its debut tonight.

Williams plays 'Marnie' on 'Girls,' which deals with everything from dating troubles to career issues in a wry manner that has been compared to both 'Sex and the City' and 'Entourage.' In addition to 'Girls,' Allison Williams has been featured in 'Will & Kate: Before Happily Ever After' and 'The League.' With talent and appeal stretching far past her appearance,  expect to see more of Allison Williams in the years to come.