Mads Mikkelsen has admitted in the past that he's at the very least a casual gamer, and broadly considers Kojima to be "the master" of the craft. When Kojima approached him for the role, he didn't even have to consider it. The relationship also goes both ways, as Kojima considers Mikkelsen to be the greatest actor alive and is a dream come true to work with him.
Development of Death Stranding was so smooth that Sony Interactive Entertainment stated that they've never seen a game made at such a fast pace.
Hideo Kojima and Norman Reedus appeared at the 2017 Game Awards and walked on the stage after the premiere of the new Death Stranding trailer. When Hideo said that the two of them were working together again, Norman said, "And nothing is gonna stop us this time!" This is referencing Konami's mistreatment of Kojima and the cancelled Silent Hills project.
Guillermo del Toro is providing his likeness to a character, who is to be motion-captured and voiced by somebody else. According to del Toro, he is Kojima's "puppet" and he has no idea what his role in the game will be. This is likely the collaboration he and Hideo Kojima were referring to after the cancellation of P.T. (2014) by Konami.
Keanu Reeves was one of the people who was considered to be in the role of Cliff, but Kojima chose Mads Mikkelsen instead.