Short answers, pulled from the story.
Box Office Mojo was founded by Brandon Gray, who began running the site on the 7th of August 1998. Gray started by publishing weekend box-office forecasts for the top ten highest-grossing films in the United States.
Box Office Mojo is owned by IMDb, which is itself a subsidiary of Amazon. Amazon purchased Box Office Mojo through IMDb in July 2008.
Box Office Mojo by IMDbPro is the rebranded name the site adopted on the 23rd of October 2019 following a major redesign. The rebrand also moved several data features, including franchise, genre, actor, and budget figures, behind the IMDbPro subscription paywall.
Box Office Mojo covers box office results from up to 107 countries and tracks the weekly box office of 50 countries in its international section.
Yes. Box Office Mojo introduced a subscription tier called Premier Pass in 2003, which limited certain data to paying subscribers. After Amazon acquired the site in 2008, Premier Pass features became free, but a new paywall returned with the 2019 redesign.
The Box Office Mojo forums ran from 2002 to 2011 and had more than 16,500 registered users. They were officially closed on the 2nd of November 2011, and users were invited to join IMDb's message boards, which themselves closed on the 20th of February 2017.