Nicotine carries the name of a diplomat who never knew it existed as a chemical.
Jean Nicot de Villemain was born in 1530 and died in Paris in 1600 or 1604, depending on the source. He was a French ambassador in Lisbon. In 1560, Europeana says, he is credited with bringing tobacco to the French court, having carried plants from Portugal because he believed they had medicinal value. Etymonline gives a slightly different date and says that in 1561 he sent tobacco seeds and powdered leaves from Lisbon to France.
Snuff became fashionable among the nobility, and Europeana says Nicot became a celebrity. A tale that he cured Catherine de' Medici's migraines with it circulates, but the only support is a cigar guide, so it is left out here. Wikipedia notes that the friar André Thevet claimed that he, not Nicot, introduced tobacco to France.
The plant name came next. Europeana says the botanist Dalechamps called tobacco Herba nicotiana in 1586, a name Carl Linnaeus later adopted. Britannica says Linnaeus named the genus Nicotiana in Nicot's honor in 1753. So the honor was already in use before Linnaeus made it formal.
The chemical came much later. Etymonline records English nicotine from 1819, from French nicotine, earlier nicotiane, from Modern Latin Nicotiana. Europeana says German chemists Wilhelm Heinrich Posselt and Karl Ludwig Reimann isolated the compound in 1828, believing it a poison. The sources do not explain the gap between those dates. The surname Nicot is itself a diminutive of Nicolas.
So the compound that drives tobacco addiction is named for a plant that an ambassador sent home as medicine. The sources disagree on some of his dates, which is why the dates above are attributed.