The record-breaking name, now thought to be the world's longest, was the idea of music graduate George Garratt, 19.
He changed his name by deed poll online for £10 last week.
Captain Fantastic said: "I wanted to be unique.
"I decided upon a theme of superheroes."
Captain Fantastic joins a number of people with unusually long names, including Rhoshandiatellyneshiaunneveshenk Koyaanisquatsiuth Williams, a girl born in Texas in 1984.
The teenager, from Glastonbury, Somerset, added that while he thought the new name was "crazy", his grandmother was no longer speaking to him.
Last month in Italy, a couple was banned from naming their son Friday - Venerdi - because the name could expose him to ridicule.
Named after the manservant of Daniel Defoe's famous novel Robinson Crusoe, the court ordered the boy's name be changed to Gregorio, named after the saint's day on which he was born.
In February, a judge in New Zealand made a young girl a ward of court so she could change her name from Talula Does The Hula From Hawaii.
Other banned names include Sex Fruit, Keenan Got Lucy and Yeah Detroit.
In New Zealand again, last year a couple was banned from naming their baby 4Real, so they chose Superman instead.