Family name Thadeu (Thadeu 
) , all over the world, is a rare surname. The cognomen Thadeu is characteristic of Portugal, where it is a rare surname, Brazil, and Chile, where it is an extremely rare surname. Not in comparison with a country's population, this name is the most popular in Brazil, Portugal, and the United States. More frequently, Thadeu is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Thadeu | Brazil, Portugal, United States, Germany, Philippines |
| décio thadeu Professor of Geology, Instituto Superior Técnico, Lisbon (b. 1919) |
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| márcio thadeu Brazilian economist, BR (b. 1962) |
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