I'm not sure there is any one person who fulfills this role but it seems like both Ryan Meinerding and Charlie Wen would take that role as they have been labelled as Heads of Visual Development at Marvel Studios. According to IMDb:
Ryan Meinerding is the Head of Visual Development at Marvel Studios. He has been with Marvel Studios since the early days of 'Iron Man,' helping to design the look and feel of the Marvel Cinematic Universe.
Pioneer of Visual Storytelling for over two decades for the entertainment industry's largest franchises, including 4 worldwide top 10 Films and triple A games. Charlie's unrivaled creative leadership in story, character, and world creation has culminated in global smash hits such as Marvel's The Avengers, Guardians of the Galaxy, League of Legends, and God of War. He is most known for co-founding and heading Marvel's Visual Development, and was accountable for designing the look and feel of the Marvel Cinematic Universe since Thor in 2008.
By 2009 Charlie was invited by Marvel Studios, where he founded and headed Marvel's Visual Development department with Ryan Meinerding. As a department co-head, Charlie was responsible for designing and integrating the look and feel of Marvel's innumerable iconic heroes and villains from divergent realms into one cohesive cinematic universe. He was also in charge of inspiring future scripts through the visual storytelling of keyframes, art-directing the costume department and visual effects houses. His films include Thor, Captain America: the First Avenger, Marvel's The Avengers, Iron Man 3, Thor: the Dark World, The Guardians of the Galaxy, Captain America: Winter Soldier, Avengers: Age of Ultron, Ant-Man, and early art-direction of Black Panther.