Short answers, pulled from the story.
ICAO traces its formal origin to the Chicago Convention, signed by 52 countries on the 7th of December 1944. The provisional organization, PICAO, began operating on the 6th of June 1945, and ICAO became a full United Nations agency in October 1947.
ICAO is headquartered in Montreal, Quebec, Canada. In June 2014, the Montreal Metro station nearest the headquarters was renamed Square-Victoria-OACI to mark the 70th anniversary of ICAO's presence in the city.
ICAO has 193 members, comprising 192 of the 193 UN member states plus the Cook Islands. Liechtenstein is the only UN member not directly in ICAO; it delegated Switzerland to enter the treaty on its behalf in 1947.
CORSIA, the Carbon Offsetting and Reduction Scheme for International Aviation, was finalized on the 6th of October 2016 among 191 ICAO members. It uses carbon offsets to address international aviation emissions, targets a 50% reduction by 2050 relative to 2005 levels, and remains voluntary until 2027.
In January 2020, ICAO blocked accounts belonging to think-tank analysts, U.S. Congressional staff, and journalists who had mentioned Taiwan in posts related to the COVID-19 pandemic and Taiwan's exclusion from ICAO safety and health bulletins. ICAO said it acted to protect the integrity of information on its feeds; the U.S. Department of State called the action outrageous and unacceptable in a press release dated the 1st of February 2020.
ICAO uses four-letter airport codes based on geographic region and country, while IATA uses three-letter codes that are generally unrelated. For example, Charles de Gaulle Airport is LFPG under ICAO and CDG under IATA. In the continental United States, ICAO codes usually add the prefix K to the IATA code, making Los Angeles International Airport KLAX.