Conversation so far:
What type of visual effects were used in this movie?
Using CGI techniques, it was possible to depict Gump meeting deceased personages and shaking their hands.
What other techniques were used?
To record the voices of the historical figures, voice actors were filmed and special effects were used to alter lip-syncing for the new dialogue.

Question: Who was in charge of the visual effects?
Self-contained rewrite: Who was in charge of the visual effects for the movie Forrest Gump?