The Tyler precedent refers to the example set by John Tyler. John Tyler was Vice President to William Henry Harrison. Harrison was elected US president in 1841. However, he died after only 30 days in office. This created a problem, as this was the first time a US President died in office. Since there was no rules on this, John Tyler established the precedent (example) that the Vice President will then take over if the President passes away or becomes unable of performing the duties of a president. Even though he sets this example in 1841, the constitutional amendment that makes this official is not seen in the US constitution until 1967. This Tyler precedent becomes law officially with the 25th amendment.