He asks players to find his family treasure.
Patrick Garrett is a reference to the 1973 movie Pat Garrett & Billy the Kid. The real life Pat Garrett (1850-1908) was a lawman in the American Old West and is best known for killing Billy the Kid in July 1881.
Standing near Patrick Garrett is the Undercity flightmaster, Michael Garrett. Although there is no explicit evidence of a familial relationship between the two, if it assumed that Patrick is Michael's son, then Patrick is the "Bat Master's son". This would be a play on the words Bat Masterson, another lawmen of the American Old West, William Barclay "Bat" Masterson (1853-1921).