Hank Pym's old assistant, who has his own version of every story Pym tells, and a girl to save.
Bill Foster is a physicist who was Hank Pym’s assistant on Project Goliath and the Giant-Man of his day. Laurence Fishburne plays him. In 2018 he is teaching quantum physics at UC Berkeley when Pym, Scott Lang and Hope van Dyne come looking for help, and the film gets a great deal out of two old men who each remember the other as the difficult one.
He is also the surrogate father of Ava Starr, the Ghost, since her own father Elihas died, and everything he does in the film is for her. When Ava restrains Pym, Lang and Hope, Foster explains that he has been working to cure her by drawing quantum energy from the Quantum Realm. Pym knows the plan would wreck the rescue of Janet van Dyne, and the three of them get away.
Minor spoiler
Pym talks him down before going into the Quantum Realm, and promises to find another way to help Ava, and his ants escort Foster out. When Janet is rescued she gives Ava some of her own energy to stabilise her, and Foster takes Ava away, with Pym still promising a permanent cure.
Show detailsA variant
A different Foster, as Goliath, appears in the animated What If…?, which this catalogue does not count for live-action characters.