In this Spanish name, the first or paternal surname is Brain and the second or maternal family name is Peña.
Matias "Mati" Brain Peña (born January 15, 1974, in Santiago) is a Chileantriathlete. Nicknamed "Mati", Brain competed at the first Olympic triathlon at the 2000 Summer Olympics. He took forty-first place with a total time of 1:53:44.90.