Why was the presidency of John Tyler significant?

John Tyler served as president from 1841 to 1845. His presidency was most significant because it established a precedent for presidential succession. He was the first vice president to become president after a sitting president's death.
In 1840, Tyler, a Virginian, was selected as the Whigs vice presidential candidate in an effort to win votes in the South. The Whigs' campaign slogan was "Tippecanoe and Tyler, too." William Henry Harrison, the presidential candidate, had won a famous battle over the Indians at Tippecanoe in 1811.
The Whigs won the election, but Harrison died only one month into his term. Should Tyler remain vice president and merely carry out presidential duties? Tyler rejected that idea and assumed full presidential powers. He was called "His Accidency" by critics. After Tyler vetoed a couple of bills favoring a national bank, the Whigs disowned him. He became a president without a party.
Undaunted, Tyler sedulously carried out his presidential duties. He ended the Second Seminole War in Florida and put down Dorr's Rebellion. He also strengthen the navy.
https://www.britannica.com/biography/John-Tyler