Lin-Manuel Miranda is a good friend of the McElroys' and best known under his alias, the Fourth McElroy. Some say he will truly ascend when he finally adopts the McElroy name and his initials become LMMM. He wrote a musical that Griffin McElroy almost shat his pants during. 
He is the brother's #1 fan and the most prominent user of the Greatjob horn.
Personal life Edit
Lin has made musicals such as In the Heights (2008) and Hamilton (2015). He worked on Moana and later on on Mary Poppins Returns, hell yea get that Disney experience boy
In 2014 he appeared as a guestspert on MBMBaM 193: Journey to the Center of the Bear, where he gave some actual advice (a possible first ever for MBMBaM) and wrote the brother's a song called "Fugue For Brotherhorns." It was hauntingly beautiful. 
Hey do you think since he listens to MBMBaM constantly he knows what vore is
In 2016 he and Travis McElroy had a battle of the gods, where Travis attempted to take Lin's Tonys even though he very much did not yet deserve them. The fight conceded after 7 days and 6 nights, with both forces having found a mutual new respect for each other.
Griffin has also declared he will remove the medallion from one of Lin's Tonys and will use it as "the world's most radical and the world's most prestigious Tony bony pog slammer."
In 2017 he was robbed of an Oscar, and Griffin announced that their friendship with Lin was ended, La La Land is now their new best friend. 
In 2019 we will know what to fear.