Who was the First Person into Space?

Time was when we believed that Yuri Gargarin in April 1961 became the
first person to go into space. Since then, however, the question of
just how far up do you have to go before you're in space has been
raised. The answer given, as I understand it, is that you're in space
when you're above 99.9% of the mass of the Earth's atmosphere. This
height, I think, is about 50 miles (262,000 feet).

I have heard that some X-15 pilot achieved this altitude before Yuri
Gargarin's flight and therefore had become the first person into
space, although without he or anyone else knowing it at the time. The
first X-15 flight to exceed 200,000 feet did not take place, however,
until October 1961, according to the X-15 chronology on the NASA web
site http://www.hq.nasa.gov/office/pao/Hi...15/chrono.html, which was
some months after Gargarin's flight.

My assumption about space beginning, as it were, at an altitude of 50
miles might be incorrect. If it is then, what altitude do you have to
achieve before you can be considered to have been into space? Is this
story about an X-15 pilot true, then? If so, who was the pilot, what
altitude did he achieve and on what date?

If my assumption is correct, on the other hand, then it would appear
that the story I heard about an X-15 pilot beating Gargarin into space
would not be true. However, it is interesting to note that the Guiness
Book of World Records (for 2002) gives such firsts as the first woman
into space and the first man on the Moon, but makes no mention of the
first person into space. It makes me wonder, then, just who was the
first person into space?