The political theory of the separation of powers requires legislators to be different individuals from the members of the executive and the judiciary. Certain political systems adhere to this principle, others do not. In the United Kingdom, for example, the executive is formed almost exclusively from legislators (members of Parliament) although the judiciary is mostly independent (until reforms in 2005, the Lord Chancellor uniquely was a legislator, a member of the executive (indeed, the Cabinet), and a judge, while until 2009 the Lords of Appeal in Ordinary were both judges and legislators as members of the House of Lords, though by convention they did not vote in the House until retirement).
In continental European jurisprudence and legal discussion, "the legislator" (le législateur) is the abstract entity that has produced the laws. When there is room for interpretation, the intent of the legislator will be questioned, and the court is supposed to rule in the direction it judges to best fit the legislative intent, which can be difficult in the case of conflicting laws or constitutional provisions.
The local term for a legislator is usually a derivation of the local term for the relevant legislature. Typical examples include
The generic term "deputy" may also be used, deriving from the concept that the legislator is "deputising" for the electorate of his electoral district.
Some legislatures provide each legislator with an official "substitute legislator" who deputises for the legislator in the legislature if he or she is unavailable. Venezuela, for example, provides for substitute legislators (diputado suplente) to be elected under Article 186 of its 1999 constitution. Ecuador and Panama also have substitute legislators.