Mark Fredrickson is a well-established illustrator whose clients include Time Magazine, Sports Illustrated, The Village Voice, Business Week and Mad Magazine.
His range of style reaches from straightforwardly realistic to highly exaggerated caricature. At times, he walks a line between portraiture and caricature, as in his portrayal of Phillip Seymour Hoffman (above, top).
All of Fredrickson’s work is highly finessed, with great attention to the modeling of form and the drama of lighting.
My understanding is that he worked for many years in traditional airbrush before switching to digital painting.
I don’t know of a dedicated site or blog for Fredrickson, but you can see a good selection of his work on the site of his artists representatives, Gerald & Cullen Rapp.