The important contribution is not in the simple algorithm (which I suspect others have come up with before, and I know others have independently come up with after):
Rather, it was what Lempel and Ziv proved about both of their simple algorithms -- The one published in 1977, usually referred to as LZ77 which is the basis of all <length,distance> variants, and the one published in 1978, usually referred to as LZ78 which is the basis of LZW, and other <word,char> variants.
They proved that for a very large class of sources (those described by markov models, context trees, among many others), these algorithms asymptotically give the best possible compression. In fact, some applications (also proved correct by Ziv) use the compressed datastream statistics to estimate source entropy, because it's much easier to implement than any direct measurement.
Both Ziv and Lempel did a lot of other things; However, Lempel did more in the area of switching systems and his other contributions are numerous and interesting, but were less profound in any specific field -- Whereas Ziv's contribution to Information Theory through the last 60 years or so has been much more profound.
Rather, it was what Lempel and Ziv proved about both of their simple algorithms -- The one published in 1977, usually referred to as LZ77 which is the basis of all <length,distance> variants, and the one published in 1978, usually referred to as LZ78 which is the basis of LZW, and other <word,char> variants.
They proved that for a very large class of sources (those described by markov models, context trees, among many others), these algorithms asymptotically give the best possible compression. In fact, some applications (also proved correct by Ziv) use the compressed datastream statistics to estimate source entropy, because it's much easier to implement than any direct measurement.
Both Ziv and Lempel did a lot of other things; However, Lempel did more in the area of switching systems and his other contributions are numerous and interesting, but were less profound in any specific field -- Whereas Ziv's contribution to Information Theory through the last 60 years or so has been much more profound.