The thought of symbiotes tends to conjure images of vicious villainous characters like Venom, Carnage, Toxin, and Scream. However, in 2015, a team of symbiotic characters were introduced who actually served as protectors of the Marvel Universe.
The Agents of the Cosmos first appeared in the Venom: Space Knight series by Robbie Thompson, Ariel Olivetti, Aaron Kim Jacinto, and Gerardo Sandoval, which ran for 13 issues starting in November 2015 and ending in October of 2016.
The circumstances that led to the team's formation were revealed in Venom Vol 4 #4 by Donny Cates, Ryan Stegman, JP Mayer, and Frank Martin with Thor playing a major role. Knull, the evil cosmic deity who created the symbiotes in the Marvel Universe, had created two symbiotic dragons called Grendel and Big Mother, which headed to Earth and started slaughtering people in Denmark, as part of a plan to subjugate the planet. Thor intervened just as the two dragons began to bond themselves to benevolent hosts, striking Grendel with a blast of divine lightning so potent that it severed Knull's connection to the majority of his symbiotic subjects. However, the hive mind associated with all the symbiotes had already been tainted with goodness, courtesy of the noble people the dragons had bonded with, which led some of the symbiotes to rebel against Knull. They imprisoned him at the centre of his throneworld and renamed it "Klyntar", which was their word for "cage" and formed a team or an order, known as the Agents of the Cosmos.
Using their ability to sense the "voice" of the cosmos, the group would go on to attempt to make amends for their species' dark history by recruiting worthy hosts, in the form noble warriors from across the universe, and pledging to protect the reality they had previously tyrannized and tormented. While helping the hopeless and oppressed, they would also attempt to maintain the lie that their species had always been benevolent, to erase the very memory of their past and avoid unnecessary conflict. Throughout the course of their existence, their members included the likes of Myntril (an alien of unspecified species), Tarna (a Skrull), and none Earth's Eugene "Flash" Thompson, the human who famously bonded with the Venom symbiote and became Agent Venom.
Inadvertently, some symbiotes ended up bonding with unworthy hosts who proceeded to go against the team's directive, opting to use their powers for malevolent purposes and even though these rogue individuals were cut off from the group and supposedly stopped, they were capable of replicating themselves through a process of asexual reproduction and promptly went back to fulfilling Knull's evil wishes of violence and conquest. The Agents of the Cosmos' response to this was to develop a process, using their hive mind, to cleanse the rogue symbiotes by purging all negativity and malevolence from their memories. However, it wasn't always as effective as they'd like and symbiotes who weren't fully cleansed were left in constant danger of relapse. Symbiotes that were still considered to be potential threats would be forced to undergo a trial on their homeworld to determine their fate and they would either be executed or allowed to continue with their noble duties, depending on the outcome of their trial.
The group in its classic form disbanded and its remaining members were seemingly wiped out by a species of crystalline alien beings known as the Poisons. However, there is a chance that some of them escaped the assault, meaning there's also a slight chance of seeing the Agents of the Cosmos reappear again one day.