It's amazing how something useful and innovative gets invented, and isn't so much as documented, let alone patented or published in a journal.
LZ4 is only one of the many variations on the basic principle of the LZ family of algorithms, which is to replace repeated sequences with references to where they were before.
What does amaze me a little, is the fact that the rather more complex Huffman algorithm was published and implemented decades before LZ.
The core idea of LZ, however, has been known for centuries: https://en.wikipedia.org/wiki/Iteration_mark
This is true, there is low algorithmic novelty in lz4.
However, that's missing the point: lz4's decompressor is simultaneously simple and also the fastest thing aroud, at least at the moment.
In fact, it is so fast, it can be used to accelerate local data transfers over "slow" links like bonded 10GBit ethernet and arrays of PCIe SSD's.
The proprietary LzTurbo [0] and free Lizard [1] both claim to be faster at decompression while having better compression ratios.