Short answers, pulled from the story.
The OECD officially superseded the OEEC in September 1961 after the Convention on the Organisation for Economic Co-operation and Development was signed on the 14th of December 1960. The first Secretary-General of the OECD, Thorkil Kristensen, began his term on the 30th of September 1961.
The official founding members of the OECD were Austria, Belgium, Canada, Denmark, France, West Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, the United Kingdom, and the United States. Three countries, the Netherlands, Luxembourg, and Italy, ratified the OECD Convention after September 1961 but are nevertheless considered founding members.
Finance officials from 130 countries agreed on plans for a new international taxation policy known as the global minimum corporate tax of 15% on the 1st of July 2021. All major economies agreed to pass national laws that would require corporations to pay at least 15% income tax in the countries they operate.
Mathias Cormann, an Australian, has served as Secretary-General of the OECD since the 1st of June 2021. He succeeded José Ángel Gurría from Mexico, who served from the 1st of June 2006 to the 31st of May 2021.
There are 38 members of the OECD as of the latest reporting period. The organization has expanded significantly since its founding to include countries such as Chile, Slovenia, Israel, Estonia, Latvia, Lithuania, Colombia, Costa Rica, and others.