Who sings it?
That would be Rodrigo Amarante, a Brazilian singer-songwriter who's been on the music scene since the late '90s. He got his start in the Rio de Janeiro-based band Los Hermanos, then joined Little Joy, which paired him with the Strokes' Fabrizio Moretti. He went solo in 2014 with the album Cavalo. You can hear a few tracks off that record via NPR's Tiny Desk Concert series. (Fun fact: the guitar Amarante plays there has a name, and it's Butter.)
Narcos producer José Padilha was familiar with Amarante's music because his cousin made a documentary about Amarante's band. But Amarante had also worked with Wagner Moura, who played Escobar on the show (RIP), on a Brazilian production of Hamlet. With recommendations from both Moura and Padilha, Amarante was a natural pick for the title music.
To write the song, Amarante turned to an unlikely inspiration: Escobar's mom. "I had this idea to write a song that was his mother's favorite when he was a kid, something that would influence his idea of the man that he would like to be," Amarante told Billboard. "I wanted to deliver something romantic and deceivingly generous but if you listen to the lyrics you see that there's a narcissistic point of view. The show is about cocaine and gangsters, so I could easily write a song that's heavy and nervous and Latin. But how would that expand the story?"