Michael Mamaril is an NPC who spends his days roaming Sanctuary giving out free gear and guns to vault hunters! Once you reach Sanctuary, he will be in one of ten random spots so you may have to play hide and seek. He may not give you something every time you approach him, but when he does, it is usually fairly decent stuff. Also note that if you are in a party, only ONE person will receive something from him at a time, not the whole group so you may have to dashboard, save, repeat if you are in a party.
Below is a description of the areas he can spawn at
In the back room to the right, next to the jukebox.
Next to the slot machines.
From the Sanctuary entrance, head up the right staircase and immediately turn right.
Bottom level on the right side, under the stairs.
Bottom of the stairs.
On the corner, by the front door of the black market.
(opposite Moxxi's side entrance)
Dead center of the room.
Crimson Raiders HQ
Upon entering, directly in front of you, between the stairs and Tannis's workshop.
Opposite Paradise Station, next to the newspaper stand.
Top of the staircase, on the left.
HAPPY HUNTING AND GOOD LUCK!