Here's what I can assemble from a number of magic publications:
He was born in or around 1891, and by 1910, persuaded his father to use money that had been saved for college to study magic, eventually performing under the names The Great Gilland, Don Cortex and Tex McGuire. His favorite trick consisted of driving a Cadillac, with seven passengers, on stage and making the car and its occupants disappear. By age 19, he began traveling with a show headed by Mrs. Tom Thumb. He served in WWI, wounded and subject to gas attacks. In the 1920s, he returned to Europe. And here's where the legends begin.
The list of bank breakers -- though admittedly incomplete, does not include McGuire's name. Another myth swirling around McGuire was whether he (like so many others) was the author of The Phantom of the Card Table. That McGuire might be Erdnase is further undermined by a second rumor associating him with Walter Scott, an individual who is claimed by some to be that elusive writer.
One of McGuire's most important contributions to magic occurred, in a sense, posthumously. Beginning in 1922, he entered into a long, detailed correspondence with the famed T. Nelson Downs. The two men wrote a series of letter that were meticulously cataloged over several years, exchanging trick ideas, moves, handlings and stories. In 1971, John Braun compiled these ideas into a special Linking Ring parade which is quite interesting.
I originally picked up this oversized, two-color, single-sided business card because I knew of McGuire as Max Malian's manager (and I having a copy of what seemed to be McGuire's manager card). After researching this subject, though, I no longer know what to believe.