Overview
A formateur (French for "someone who forms, who constitutes") is a politician who is appointed to lead the formation of a coalition government, after either a general election or the collapse of a previous government. The role of the formateur is especially important in the politics of Belgium, the Netherlands, Luxembourg, Italy, Israel and the Czech Republic. These countries have a parliamentary system, where the executive derives its mandate from majority support in the legislature. They also use proportional representation for elections to parliament, and have a multiparty system that makes it improbable for one party to win an outright majority. There may be several combinations of parties which might form a coalition. The Formateur is traditionally appointed by the head of state but in the Netherlands that became the right of the Speaker of the Lower house ('president of the Second Chamber') in the early 21st century.
The formateur most often comes from the largest party in the future coalition (although an even larger party may remain in the opposition) and generally becomes the new head of government if the formation succeeds. Under a constitutional monarchy this appointment may be a reserve power of the monarch, and remains one of the rare moments when a mostly ceremonial monarch may play a significant political role.
In game theory and political science, the term formateur party is used to describe the party that makes a proposal in a bargaining process, most often when modeling a government formation.
Informateur
The formateur's work may be preceded by one or more informateurs, also appointed by the same authority as the formateur. The informateur is not expected to finalize a coalition, but attempts to find enough points of agreement to identify a likely coalition, from which a formateur is then selected to conclude a political program and compose a cabinet, usually headed by himself. The informateur should be someone not otherwise considered for ministerial office, although some do obtain a portfolio in the future government. The role is often filled by a retired statesperson of some stature, often a former government minister or party leader.
From Wikipedia (CC BY-SA 4.0).