19th century slang which was popularized more recently by the movie Tombstone. Means "I'm the man you're looking for". Nowdays it's usually used as a response to a threat or challenge, as in the movie.

Intelligence agency term for "psychological operation". A government or corporate-sponsored operation, usually taking the form of a "terrorist attack" or "crazed gunman on a spree", with the intent of panicking the public into demanding more police and laws inhibiting freedom. Psyops are usually carried out by drugging a civilian or group of civilians with aggression-promoting drugs, psyching them up, arming them, and sending them out to commit mayhem. Government-sponsored terrorism. See also blackshirts, conspiracy

The etymology of the phrase is traced back to Aurthurian Lore. Huckleberry Garlands were said to be given to Knights of the Kingdom for coming to the service of a damsel. They would approach the lady, lower their lance, and receive the small branch as a symbol of gratitude; much like a medal.
Therefore, "I'm Your Huckleberry" literally means "I'm your Hero."
In current adaptaions, in reference to the movie Tombstone, it means "I'm your man." as an affirmative response to a challenge.

"

RINGO:

Wretched slugs, don't any of you

Have the guts to play for blood?

O.S. VOICE:

I'm your huckleberry.

Ringo turns. Doc stands there, smiling that Cheshire cat

smile.

DOC

That's just my game.
"
Taken form the offical script from the movie Tombstone.

I'm your huckleberry comes from a very classic and hot western movie called tombstone. this phrase means I'm the perfect man for the job.

All these responses are silly assumptions!
In the moveie he didn't say "I'm your huckleberry", he said "I'm your HUCKLEBEARER". His accent in the movie makes it hard to hear. In the 1800's little handles on a coffin were called "huckles", an English term. Instead of pallbearers the people who carried the coffin were called "hucklebearers" at the funeral.
This is why the other guy got so bent outta shape when Doc said "I'm your hucklebearer". He was telling the other guy "I'm your pallbearer" or literally I'm causing your funeral. This is why it was so offensive and the shooting started.

A way of expressing one's commitment to lend a hand.

You play 'Tom Sawyer' and I will be your 'daddy' in this game as Tom 'kinda' looked up to Huck (in my humble opinion). Ala Mark Twain.

And I will jump into your game Like 'Huck Finn', and give you a "shel·lack·ing" (As the most Hon. Sir Sean Connery could only say properly). And we will "tear-this moTHa-out". +))