Michael Mamaril will give you ether a Blue/Purple/Legendary weapon he is located at random points around sanctuary.
His spawn locations can be found here: http://imgur.com/rFVQowp
It is best not to try to farm for Michael as you will most likely see him whilst roaming Sanctuary but if you do insist on farming him (from what I have read online) He has a 10% chance of spawning before Sanctuary is in the air and a 8% chance whilst in the air. When you do find him simply talk to him he will say something then hand you a weapon, pick up the weapon then BOOM achievement
And for those who do not know Michael Mamaril was a Borderlands fan who unfortunately died at the age of 22 in October 2011 his friend Carlos sent Gearbox an email to ask that Claptrap (His favourite character) read a eulogy. Gearbox also promised that Michael would be in Borderlands 2 as a tribute
R.I.P Michael Mamaril