From the citation: "The 2012 Leroy P. Steele Prize for Mathematical Exposition is awarded to Michael Aschbacher, Richard Lyons, Steve Smith and Ronald Solomon for their work, The classification of finite simple groups: groups of characteristics 2-type, Mathematical Monographs and Surveys, 172, American Mathematical Society, Providence, RI 2011. In this paper, the authors, who have done foundational work in the classification of finite simple groups, offer to the general mathematical public an articulate and readable exposition of the classification of characteristic 2 type groups." 

Our congratulations to Professor Solomon and his coauthors!