Probably the most representative Progressive-Art Rock band ever.
Albums like Nursery Cryme, Foxtrot and Selling England By The Pound are absolute masterpieces of 20th century's music.
The only real Genesis is the Mk2 lineup: Peter Gabriel (voice, flute), Steve Hackett (guitar), Mike Rutherford (rithm guitar, 12 strings guitar), Tony Banks (keyboards) and Phil Collins (drums, backing vocals). After Gabriel's and Hackett's departure (respecctively in 1975 and 1977), the band committed the most disgusting musical suicide of all times. Under the influence of Collins, Genesis kept the original name but threw away a decade of good music and intellectual honesty by becoming a ridiculous pop band. People who declare to prefer the Collins-era Genesis are likely to be fucking morons or not interested in good music at all, thus deserving the title of fucking morons anyway.
Gabriel and Hackett then started a fruitful and highly appreciated solo career, while Collins began writing corny, useless love songs.
Banks released some solo works too; nothing interesting or musically relevant, though. Rutherford formed pop rock group "Mike and The Mechanics", a forgettable easy listening hits factory.
If you put a bunch of progressive-rock lovers into a room and asked them to vote for their all-time favorite classic prog group, I suspect that Genesis would win handily. A perfect example of this popularity is the fact that no other group has so strongly influenced the so-called neo-prog bands of the 80s and 90s. When it was time for prog to make a comeback, it was mostly Genesis to which the new young musicians turned. Would there even be a Marillion, Pendragon, IQ, Citizen Cane, Jadis, Magellan, Glass Hammer, Cairo, Crucible, Like Wendy, Flamborough Head, Sylvan, or Metaphor (to name only a few) if there had never been a Genesis? No way!