What is the Watergate scandal which led to resignation of ex-US Prez Richard Nixon?

Watergate scandal was one of the biggest political scandals in US history involving ex-President Richard Nixon. In 1972, five men linked to Nixon’s re-election campaign were caught breaking into Democratic Party’s headquarters at Watergate complex, trying to steal documents and tap phones. The scandal exposed Nixon's role in the cover-up, making him the first US President to resign from office.