Harriet (c. 1830 – June 23, 2006) was a Galápagos tortoise (Geochelone elephantopus porteri) who had an estimated age of 175 years.
Up until the day that she died some skeptics didn't believe that she had actually known Charles Darwin. DNA analysis proved that she was in fact over 170 years old but it also proved that she was from a species restricted to an island that we know Darwin never visited. Harriet is a land tortoise so it is highly unlikely that she swam to Santa Maria Galápagos only to be trapped by Darwin and spirited back to England. The island were Harriet was collected back in 1865 actually didn't have any native turtles because the white man had killed off the indigenous species to feed the prisoners sequestered there. (Skeptics stop reading here).
It seems that she was capture on her native Santa Cruz island and brought to Santa Maria where Darwin snatched her off the self at the super market. One of three tortoises taken back to England by Darwin, Harriet eventually made her way to Australia to live out her last century.
Check out the authoritative entry in wikipedia.