Nick Walker ( 1969 - ) is a British Street Art graffiti painter known for merging freehand work with stencilled imagery. Nick Walker s works have been put up for auction numerous times, with realized prices greatly surpassing estimated prices, varying from 281.96 USD for Mona Simpson in 2008 to a remarkable record 18455.86 USD for Mood board from 2005-2007 in 2008 , based on the size and medium