Gilby recognized Tommy Kirk, who was discovered by Walt Disney and became a "Mouseketeer" in 1955. He co-starred in "The Hardy Boys" serials and starred or co-starred in several big Disney films including Old Yeller, The Shaggy Dog, Swiss Family Robinson, The Absent-Minded Professor and others...he was dropped by Disney in the mid-60s and has made the occasional low-budget picture over the years.
Great work Gilby!
Mystery Man #1 - the clues: After supporting roles in the films of two big stars, this actor's credits steadily improved.
Anonymous and KC recognized Cary Grant with just one picture and one clue. Cary had supporting roles with Marlene Dietrich and Mae West and got noticed...The Awful Truth was the film that established his screen persona and his status as a major star...and he remained a top star till he stopped making films in the mid-60s (and is still a top star of classic films). Oscar-nominated for Best Actor twice, he was given a Lifetime Achievement Award after he retired.
Kudos to Anonymous and KC...