Blue Suns

The Blue Suns are a "private security organization", in reality a mercenary outfit, operating in the Skyllian Verge. The Blue Suns have a reputation for being both discreet and ruthlessly efficient, and as such charge a sizeable fee.

Blue Suns mercenaries often have a tattoo of a blue sun somewhere on their body. During high-risk jobs, the tattoo would be removed with an acid wash to prevent them being identified, then reapplied once the job was finished.

In 2165, the Blue Suns were hired by Edan Had'dah to carry out a raid on the Systems Alliance research facility at Sidon, as well as to provide security for Had'dah himself during some of his more unscrupulous activities. However, to take the job for Had'dah they had been forced to pull out of an arms deal, which attracted the attention of Saren Arterius. During his investigation he killed several Blue Sun mercs, including Groto Ib-ba. Another Blue Sun mercenary tried to arrest Kahlee Sanders under the pretence of being an Alliance MP, but she realised he was an imposter and escaped.

Later, the Blue Suns went under the command of Skarr -- despite the fact he had killed several of their number when he was first hired -- and were dispatched to intercept the SSV Iwo Jima and finally capture Kahlee. The operation was successful and Kahlee was taken to an element zero refinery. Despite the destruction of this refinery and the death of their employer, it is likely the Blue Suns as a mercenary outfit still exist.

In Mass Effect 2, the salarian scientist Mordin Solus is shown giving Commander Shepard a weapon off of a dead Blue Suns mercenary as a "bonus, in good faith", suggesting that the Blue Suns may play a role in the game. They are also seen acting as guards onboard the prison ship Purgatory.,though it is unknown how they got legal premission.

It is also revealed that the Downloadable Squadmate Zaeed co-founded the Blue Suns approximately 20 years before the events of Mass Effect 2.

Ranks
Bottom to top.

Blue Sun Trooper

Blue Suns Prison Gaurd (Onboard Prison ship Purgatory)

Blue Suns Engineer

Blue Suns Legionaire

Blue Suns Commando

Blue Suns Leader:Skarr

Trivia

 * The Blue Suns are likely named after 'Blue Sun', a corporation in the TV series Firefly.
 * They may also have been inspired by 'Black Sun', a criminal gang in Star Wars.
 * The Blue Suns have arguably the most amount of screen time and 'significance' then any other criminal organization in Mass Effect 2, alternatively taking part in or acting as the main focus of/during several missions, sub-quests or otherwise, either as enemies to be killed or antagonists to be overcome.