John Tyler is an underratedly terrible President. Only President to be kicked out of his party.
Only President to join the Confederacy. And like all of the slaveholding presidents, he was always all hat and no cattle and always stood on the brink of insolvency because of his profligate spending. Terrible president. He had principles he stuck to resolutely, but they were stupid principles.
The one meaningful contribution he made was that when Harrison died, he, without precedent, interpreted the Constitution to mean that he became the new president and didn’t continue in his capacity as Vice President. That has worked out fairly well. And as a procreator, he was unrivaled.