Alpha (Jem'Hadar)
The Alphas were Jem'Hadar who were created in the Alpha Quadrant in 2374, after the Dominion realized that no reinforcements could come through the Bajoran wormhole. 

The Alphas were genetically-engineered to fight against Alpha Quadrant species. They believed themselves to be superior to the "Gammas", Jem'Hadar who were bred in the Gamma Quadrant, leading to considerable friction between the two groups. They believed that their actions better demonstrated their loyalty to the Founders than just words. They were also more willing to take independent actions which advanced their goals, while Gammas only did what they were ordered to, and no more.

The first significant combat action of the Alphas was the brief capture of the  under Kudak'Etan. () In addition to being specifically engineered for combat against Alpha Quadrant species, Alphas had a slightly different skin tone than their Gamma counterparts, appearing to be more green and less blueish grey, as well as more prominent head crests in place of the Gammas' bone-Mohawk ridges.

List of Alphas 
 Kudak'Etan
 Lamat'Ukan

Apocrypha
 In the story of Star Trek Online, many Alphas remained in the Alpha Quadrant after the Treaty of Bajor and aligned themselves with the resurgent True Way.
It appears that there was some attempt to subtly distinguish the Alphas from Gammas in their prosthetic makeup designs. Standard "Gamma" Jem'Hadar, particularly those that appear on-screen alongside Alphas, have very prominent ridges running over the mid-line of their heads, flanked by two much smaller crests extending out from above the brows. The Alphas, in contrast, had shorter central crests, but the flanking crests were much more prominent. There was considerable experimentation with Jem'Hadar makeup designs over the seasons, however, and the Alphas only appeared in one episode, leaving it unclear if this was an official difference.

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