Part of the T206 Series issued by the American Tobacco Company (ATC) from 1909 to 1911, the Honus Wagner is the most valuable baseball card in history and has been catalogued as such since the 1930's.
While the majority of the T206 series cards were printed in the tens or hundreds of thousands, just 40 of Wagner's card reached the public. The reason for this was Wagner himself, who stopped publication of the card either because he did not want children to buy cigarettes or because he wanted more compensation from ATC.
In 1933, the card was listed in The American Card Catalog at a value of $50 - the most expensive of any listed. Since then, the value has increased exponentially with the highest recorded sale taking place in 2011 when Ken Kendrick, owner of the Arizona Diamondbacks, paid $2.8 million for an example. The card in question is not without its controversies; memorabilia dealer Bill Mastro who had previously bought and sold this particular card admitted during his 2013 trial for mail fraud that he had trimmed its edges to increase its value.