http://www.playdota.com/heroes/dragon-knight

Hero Introduction
Knight Davion is a powerful warrior who calls upon his draconic heritage to augment his already fearsome combat abilities. He has two powerful offensive skills: Dragon Tail and Breathe Fire. Dragon Tail allows him to stun a single enemy target for several seconds, and Breathe Fire taps into his inner dragon to unleash a powerful area of effect attack. This potent offense is supported by Davion's Dragon Blood passive skill, which makes him extremely difficult to kill by boosting his armor and hit point regeneration significantly. Combined together, these abilities make the Dragon Knight a tough, versatile fighter. At higher levels, the Dragon Knight gains the ability to transform completely into dragon form. The abilities and strength of the dragon form increase with levels. At maximum level, Davion transforms into a mighty blue dragon with an area of effect cold attack, which drastically slows all enemies caught in the freezing blasts. Along with his natural combat skills and toughness, this makes him an extremely dangerous foe.

Background Story
Abandoned and forsaken as a child, the Half-bred Dragon Davion sought refuge from the evils of the world, and from the uncontrollable power growing within himself. His search led him to the doorstep of a mighty Druid, who taught him to tap into the massive energies that lay concealed in his blood - a tribute to his ancient Draconian heritage. A master swordsman, Davion smites his foes in his raging frenzy - transforming at will into an Elder Dragon of destructive fiery rage to crush all those that threaten to vanquish his new home.

This is my first type writing a guide , please guide me ! (:
In my opinion , Dragon Knight is one of the more tank heroes in DotA , beside Bristleback , Axe , Centaur and etc . And feel free to comment about anything .

Skills
Breathe Fire - Breathes fire at enemy units, dealing damage.
Level - Manacost - Cooldown - Effects
1 - 100 - 12 secs - 75 damage
2 - 110 - 12 secs - 150 damage
3 - 120 - 12 secs - 225 damage
4 - 130 - 12 secs - 300 damage

Dragon Tail - Davion bashes a melee-range enemy target with the fury of a dragon's tail swipe. Stuns the target and deals minor damage.
Level - Manacost - Cooldown - Effects
1 - 100 - 10 secs - 25 Damage and Stun for 2.5secs
2 - 100 - 10 secs - 50 Damage and Stun for 2.75secs
3 - 100 - 10 secs - 75 Damage and Stun for 3secs
4 - 100 - 10 secs - 100 Damage and Stun for 3.25secs

Dragon Blood - Grants Dragon Knight blood from his ancient ancestral dragon heritage, which increases health regeneration and armor.
Level - Effects (Passive)
1 - Increases HP Regen by 1 HP/sec and Armor by 2
2 - Increases HP Regen by 2 HP/sec and Armor by 4
3 - Increases HP Regen by 3 HP/sec and Armor by 6
4 - Increases HP Regen by 4 HP/sec and Armor by 8

Elder Dragon Form - Transforms the Dragon Knight into a powerful elder dragon.
Level - Manacost - Cooldown - Effects
1 - 50 - 115secs - Transform into a Green Dragon
2 - 50 - 115secs - Transform into a Red Dragon
3 - 50 - 115secs - Transform into a Blue Dragon
Note: All level of elder dragon form lasts for 60secs.
•The Level 1 Elder Dragon is a Green Dragon that has 315 base movespeed, 500 attack range, 0.5 attack animation (0.4 backswing) and has the skill:Corrosive Breath
• Corrosive Breath takes 20 damage per second and duration 5 seconds.
• Corrosive Breath Damage type: magical
• Corrosive Breath works on structures.
• The Level 2 Elder Dragon is a Red Dragon that has 315 base movespeed, 5 bonus base damage, 500 attack range, 0.5 attack animation (0.4 backswing) and has Splash Attack. The Splash deals 100% damage in a 75 AOE, 75% damage in a 150 AOE, 50% damage in a 250 AOE.
• The Level 3 Elder Dragon is a Blue Dragon that has 315 base movespeed, 14 bonus base damage, 500 attack range, 0.5 attack animation (0.4 backswing) and has Splash Attack (same as lvl 2) and has the skill: Frost Breath.
• Frost Breath slows units for 30% movement speed and 20% attack speed, lasting 3 seconds.

Skill Build
My ideal dragon knight is tank rather than nuking ? Thus my build kinda ignores breathe fire usually .
Level 1 - Dragon Tail/Dragon Blood
Level 2 - Dragon Blood/Dragon Tail
Level 3 - Dragon Blood
Level 4 - Stats
Level 5 - Dragon Blood
Level 6 - Elder Dragon Form
Level 7 - Dragon Blood
Level 8~10 - Stats
Level 11 - Elder Dragon Form
Level 12~14 - Dragon Tail
Level 15 - Stats
Level 16 - Elder Dragon Form
Level 17~21 - Stats
Level 22~25 - Breathe Fire

(The reason i choose stats/blood over fire in order to stay lane longer to farm core items that you need .)

Items
If you pick him, you only left 600g .
Thus, go with Queling Blade, tangos and ironwood branches .
If you random-ed him, Straight away wait till you get 875g and get a ring of health .
After farming , either get a str treads or a vanguard first .
Aftermath , helm of dominator .
There you go , you're able to run lane and gank or creep stacking . If you can farm , take the chance and farm .
Get assault cuirass as soon as possible . By then you would have 40 armor . With vanguard , you're already a tank .
You can up helm to satanic or go buriza or rad for damage if you think you're lacking damage .

(PS: i'm not a good writer . Sorry :X will be back soon .)