Metafilter has announced their top posts of 2011, and one of the nominees was filthy light thief's amazing, sad, and memorable recounting last month of the life and death of Northern Calloway, who played David on Sesame Street. Calloway had struggled with bipolar disorder and, in the 1980s, increasing drug use, which created difficulties in working. He died in 1990 while at a psychiatric facility in New York.
Really, read FLT's link-laden post, and the comments from the Mr. Hooper- and David-era Street watchers. And in the mean time, here is a segment of David roller discoing through Central Park.
Northern Calloway - Sesame Street's David, 1948-1990 [metafilter]