user3597: I know how to cause a checkmate in three moves. Are there any better ones? I've been told that  there is a two move one but, I have never found someone who can do it. Is it just a legend that has happened once or twice?

user24074: You can NOT cause a mate in 3 or 2 or any low number.
If the other player is truly stupid or messing with you then it might be possible to mate in 2 for black but white to do it would take 2½

user1201: There is a two-move mate: the Fool's Mate. However, it requires White to be, as the name implies, extremely foolish!
[FEN ""]
1.g4 e5 2.f3 Qh4#

As you can see, this mate relies on White advancing pawns without any regard for his King's safety. There's no way to force a two move checkmate (if there were, Chess would be an awfully boring game!).
As to whether it's ever occurred in real (master) play, I can't find any record of it, though the Wikipedia article mentions Teed vs. Delmar, 1896, where a very similar mate is delivered a few moves later.

3597: <p>I know how to cause a checkmate in three moves. Are there any better ones? I've been told that  there is a two move one but, I have never found someone who can do it. Is it just a legend that has happened once or twice?</p>
 24074: <p>You can NOT cause a mate in 3 or 2 or any low number.</p>
<p>If the other player is truly stupid or messing with you then it might be possible to mate in 2 for black but white to do it would take 2½</p>
 1201: <p>There is a two-move mate: the <a href="http://en.wikipedia.org/wiki/Fool&#39;s_mate" rel="nofollow"><em>Fool's Mate</em></a>. However, it requires White to be, as the name implies, extremely foolish!</p>

<pre><code>[FEN ""]
1.g4 e5 2.f3 Qh4#
</code></pre>

<p>As you can see, this mate relies on White advancing pawns without any regard for his King's safety. There's no way to <em>force</em> a two move checkmate (if there were, Chess would be an awfully boring game!).</p>

<p>As to whether it's ever occurred in real (master) play, I can't find any record of it, though the Wikipedia article mentions Teed vs. Delmar, 1896, where a very similar mate is delivered a few moves later.</p>
