The Assassins Guild of New Orleans was founded by Candra. The Assassins Guild and the Thieves Guild were set in perpetual rivalry with each other by her. Hoping to gain peace, Marius agreed to marry Bella Donna, his daughter, to Remy. This agreement fell through due to Julien's interference however.
The Guild set their sights on Domino after she ditched them during a job they hired her for against The Hand. Domino set free some women that were being trafficked and stole 237 million dollars that the Guild was after. They sent Razorfist to get her, however he failed and they called Boomerang, Nakh, Clay, Black Mamba, Bullet and Bushwacker to go after her, as well as Wolverine who sided with her.
Most recently the Guild has turned its sights on Kaine as during his years as the malfunctioning clone of Peter Parker he moved in on the Assassin Guilds' turf and took on contract killings without paying tithe to the Guild. Kaine at the time blatantly refused to pay and disappeared for a years until he reappeared in Houston, now under the guise of the Scarlet Spider. After beating the killers Bella Donna sent after him, Kaine offered her a deal saying he would either do one job for her or he would kill each and every member of the Assassins Guild one by one. A deal Bella Donna accepted.
X-Men: The Animated Series
Here they appeared in the episode X-Ternally Yours. Much of their history remains the same, although not many of the guild members are seen or mentioned.
Here they are mentioned in the episode Cajun Spice, although not much is known about them other than them being a rival guild to the Thieves Guild. They are also called "The Rippers" instead of the Assassins Guild.