Leon Muss is a Twitter personality created by John Green. He believes in staying on Earth, the best planet in the known universe, and the only acceptable home for humans until 2028. John created him as part of a bet that humans would not get to Mars before 2028. If mankind doesn't get to Mars before 2028 Hank agreed to change the name of the podcast to Dear John and Hank.

Leon's Twitter account is @LeonMuss4Earth.