Possible Clues:

• He played Arnold Vinick on "The West Wing"
• Old hippie who plays an even older hippie in 'Wanderlust'
• Longtime host of "Scientific American Frontiers"
• Hawkeye Pierce's portrayer on "M*A*S*H"
• 2018 SAG Life Achievement Award honoree
• 'Bridge of Spies' co-star, 2015
• "M*A*S*H" co-star
• Tom Hanks' boss in ''Bridge of Spies''
• "M*A*S*H" star (theme hint: note the letter above every black square in each four-black square diagonal!)
• Co-star of 2019's 'Marriage Story'