Mathematics Genealogy Project - an online, search-able database of mathematicians and like-minded physical scientists with over 145,000 individual entries of mathematicians and scientists dating back to the 14th century.
My adviser's degree is in applied math (as far as I can tell British universities call theoretical physics applied math), so I have a link into the system. Here are a few of my more notable direct academic ancestors:
G.I. Taylor (2nd Great-Grandfather): Experimentally showed that the inference pattern of photons passing through a double-slit set-up persisted even if only 1 photon was present at a time; one of the early pioneers in turbulence research; famously calculated the yield of the first atomic bomb from a photo on the cover of Life magazine to within 10% (to the annoyance of the US government, who had kept the yield secret)
J.J. Thompson (3rd Great-Grandfather): Discoverer of the electron (for which he won the 1906 Nobel prize) and isotopes; inventor of the mass spectrometer; proponent of the delicious-sounding "plum pudding" model of the atom, which was tragically later shown to be inaccurate
John William Strutt, 3rd Baron Rayleigh (4th Great-Grandfather): Discoverer of argon (for which he won the 1904 Nobel Prize) and Rayliegh scattering, which explains why the sky is blue and the sun is yellow; invented the Rayleigh number, a dimensionless fluid parameter which controls the onset of convection; figured out how human ears use phase differences in sound waves to tell where a sound originates
Issac Newton (14th Great-Grandfather): Inventor of calculus and Newton's laws of motion; discoverer gravity in the scientific sense; invented and built the first reflecting telescope; originator of the corpuscular theory of light and the concept of lumineferous aether because not even Newton could get everything right
Galileo Galilei (17th Great-Grandfather): Inventor of the telescope; Father of the scientific revolution; had a little misunderstanding with the Pope; discoverer Jupiter's 4 largest moons, the phases of Venus, and sun spots (although their are some indications that Chinese astronomers beat him to it by looking directly at the sun with their bare eyes)
Like I said, everyone likes to feel a connection to the past and then tell everyone else about it.