The answer to the question - who was the charter member of the AFL 
that defected to the NFL before play began?  (You won't find this
in any "official" record books of the NFL)
 
It was the Minnesota Vikings.
 
They were hastily replaced by the Oakland Raiders.
 
Lamar Hunt founded the AFL after he was rebuffed in his attempt
to obtain an NFL franchise for Dallas.  The NFL cited an earlier
attempt to settle in Texas (the ill-fated Dallas Texans of the
early 1950s, who became the Baltimore Colts - NFL "history"
lists Baltimore as an expansion team, but it was the remnants of
the Dallas Texans).  
 
When the AFL announced that it would put a team in Dallas, 
called the Texans (just like the NFL team ten years before)
the NFL decided, gee whiz, that Dallas could use an NFL 
team after all, and so began the Cowboys.  They then turned
and got the Minnesota Vikings to withdraw from the AFL and
join the NFL.  The thinking being, if they destroy the AFL's
two wealthiest franchises, the league won't last long (ho ho ho).
 
Within a few years, the Texans moved to Kansas City and became
the AFL's most popular team.  The Raiders, of course, were the
Raiders.  There was very bad blood between the AFL owners and
the Minnesota franchise for many years.
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