Pat McAuley (sometimes known as John McAuley) was one of the many numerous players in the history of Them, which boasted one of the most unstable lineups of any major 1960s group. Sometime in mid-1964, he joined Them -- which had just started to record -- on organ, replacing Eric Wrixon. He was only on keyboards a short while before switching to drums when Them's original drummer, Ronnie Millings, left later in 1964. Around the beginning of 1965, Pat's brother, Jackie McAuley, came in on organ, though Jackie only lasted a few months, leaving in April 1965. Pat only lasted a little longer, leaving in the summer of 1965 after a shakeup that left only two original members of Them in the band, Van Morrison and bassist Alan Henderson.
Given the general havoc of musical chairs in Them between mid-1964 and mid-1965, and the presence of session men on some of their recordings, it's probably impossible to determine on which Them tracks Pat McAuley plays. Most likely, though, he's on some or all of the material they recorded between late 1964 and mid-1965, and he does appear with the band (on drums) on the sole live Them clip, of their appearance at the New Musical Express Poll Winners Concert on April 11, 1965.
Right after leaving Them, Pat McAuley got involved with a Them spinoff group that, while good, had just as complicated a history as the original Them. He and original Them guitarist Billy Harrison formed a band that also laid claim to the Them name, in competition with the Them that now included Van Morrison and Alan Henderson as the only original members. At first McAuley played keyboards in the band, which also included singer Nick Wymer (formerly of the Fairies) and drummer Skip Alan, but Harrison, Wymer, and Alan were all gone by the beginning of 1966 (with ex-Pretty Things drummer Viv Prince coming in for a brief stint after Alan left). Pat McAuley and bassist Mark Scott were at this point the only remaining original members of this group (who were still trying to claim the name Them for themselves), joined by his brother Jackie McAuley and Ken McLeod, whom McAuley had replaced in the Belfast band Echo Four Plus One back in early 1964. Also in early 1966, Pat McAuley went back to drums, with McLeod (who'd come in on drums) switching to guitar, and Jackie McAuley taking over the keyboards.
In March 1966, it was ruled that only Van Morrison's group were entitled to use the name Them in the U.K., leaving Pat McAuley's band to play under the name the Other Them (although the ruling only applied to the U.K., not other countries). They continued to struggle onward throughout most of 1966, recording an album's worth of material (largely produced by Kim Fowley) that featured quite good R&B-rock in the style of early Them. This is the album that was eventually issued in 1967 in Scandinavia as by the Belfast Gypsies, titled Them Belfast Gypsies, although the group, confusingly, never played live under the name the Belfast Gypsies, only as Them or the Other Them. By the time the LP was issued (preceded by single and EP releases in various countries), the Belfast Gypsies had broken up, disbanding in late 1966. About six months later, Pat McAuley had left music for a day job (although his brother Jackie has continued to play and record for decades), dying in Donegal in 1984.