What is Bitcoin's "genesis hash"? From Lightning Network documentation:


  Used in several of the BOLT documents to denote the genesis hash of a target
  blockchain. This allows nodes to create and reference channels on
  several blockchains. Nodes are to ignore any messages that reference a
  chain_hash that are unknown to them. Unlike bitcoin-cli, the hash is
  not reversed but is used directly.
  
  For the main chain Bitcoin blockchain, the chain_hash value MUST be
  (encoded in hex):
  6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000.


However this wiki entry about Bitcoin's genesis block has 


  GetHash()      =
  0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f


Indeed, inputting the latter value into blockchain.info yields Block 0, while the former value cannot be found on blockchain.info.

Why does the value 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 appear in Lightning Network as "Bitcoin's genesis hash"?
They're exactly the same number; one is written in little endian notation and the other is big endian.  Notice that the bytes (two-hex-digit pairs) are exactly reversed from one to the other.

Block explorers like blockchain.info usually expect big-endian for block hashes.  The proof-of-work requirement means that the most significant bits have to be zero, so big endian makes it easier to see this.