H. P. Lovecraft

Howard Philips Lovecraft (August 20, 1890 - March 15, 1937) was an American author, whose works in the horror genre have become widely celebrated and considered the most influential horror author in American history - although all of his acclaim was posthumous.

As Lovecraft had been dead decades before Teenage Mutant Ninja Turtles even existed, he very obviously had no direct hand in any TMNT projects. However, his reputation in modern times has made references to him ubiquitous and his works, including throughout many incarnations of the TMNT.

Mirage

 * Both Edgar Allan Poe and Robert E. Howard, contemporaries of Lovecraft's in real life, mention him by name in Juliet's Revenge. Howard tells that Howard's nickname for him was "Two-Gun Bob", and Poe notes that Lovecraft had been banished by Savanti Juliet to R'lyeh, which is a sunken city in Lovecraft's works where the cosmic entity Cthulhu is buried.
 * The story tones and creatures in Rocks are heavily inspired by Lovecraft's works.

IDW

 * The Infestation 2 event centered around horrors of Lovecraftian lore invading the various properties licensed by IDW Publishing. Shub Niggurath, mentioned first in Lovecraft's 1928 story The Dunwich Horror, is summoned by the antagonist Bloch. Bloch himself is named for Robert Bloch, who was personally mentored by Lovecraft and contributed to the mythos he created.

1987 TV series

 * The cult and monster appearing in Splinter No More have a distinctly Lovecraftian flavor to them.

2003 TV series

 * The Darkness Within is very heavily Lovecraft-influenced. The character of C.F. Volpehart's name is an anagram of H.P. Lovecraft. Furthermore, the Necro Monster takes many design and personality traits from Lovecraftian creatures, especially Cthulhu.

2012 TV series

 * Dr. Victor Falco heavily resembles Herbert West of the film Re-Animator. Re-Animator was based on Lovecraft's story Herbert West - Reanimator. The character is also voiced by Jeffrey Combs, who played West in the Re-Animator film series, and experiments with a green solution as West did.
 * The Daagon and Cthugga of The Cosmic Ocean are named for Dagon and Cthulhu of Lovecraft's works.