(Note the description implies a full paragon path, alternate outcomes listed below.)
Before Mass Effect 2
Zaeed Massani has earned a reputation for being one of the most dangerous men in the Terminus system. Zaeed has take on and completed impossible jobs and is typically the only survivor of these missions. Zaeed founded the Blue Suns mercenary group alongside his partner Vigo Santiago. Vigo handled the books while Zaeed lead the men into battle. The two eventually came at odds when Bugo wanted to hire Batarians as a source of cheaper labor while Zaeed thought of them as "goddamn terrorists" as refused. Vigo then directed siz of Zaeed's own men to hold him down while Vigo shot Zaeed square in the face. Zaeed survived his injury though with a noticeable facial scar and lost some depth perception. Zaeed was still a force to be reckoned with.
Zaeed's first impossible task was to lead five other men into taking down a Turian frigate "the Vekrian". Zaeed and the team were only allowed what they could carry and had to take the frigate down from the inside. They took it down though Zaeed was the only survivor and he noted that he made a bundle from the others share. Another story involves Zaeed being ambushed by a Hanar and being almost strangled to death by the jellyfish like alien, leaving Zaeed a begrudging respect for them. Zaeed also took down a leader in the Blood Pack group though this was not a job, the Krogan leader just ahppned to raid the freighter that Zaeed was traveling on. Zaeed challenged the Krogan to a one on one fight without a weapon and manager to beat him and steal his gun to kill the rest of the mercenaries. Zaeed ended up keeping the helmet as a reminder.
Mass Effect 2: The Price of Revenge
Zaeed is contacted by Cerberus and paid a substantial cash bounty in order to join Commander Shepherd's squad. When asked why a mercenary would join a suicide mission he mentions how Cerberus had paid him a lot of money. Zaeed is wrapping up his latest bounty when Shepherd finds him. A Batarian who fled to Omega. Once Zaeed has joined he sets himself up in the lower level of the ship and will often tell Shepherd stories of past exploits. Zaeed took the mission on one other condition. Zaeed was hired to retake an Eldfell-Ashland refinery on Zorya from the Blue Suns. Zaeed knows his old partner Vigo is their and 20 years of hunting is about to pay off. Zaeed lands with Shepherd and they cut through the Blue Suns easy enough. Zaeed will then expalin his grudge against Vigo and state his survival was due to his rage. "Rage is a hell of an anesthetic." When faced with Vigo and an ambush Zaeed sets the refinery ablaze in order to escape/takeout Vigo. Vigo runs for his personal shuttle and during the pursuit Shepherd and Zaeed learn that Zaeed's actions have endangered the workers of the plant. Zaeed is all for letting the group burn, but Shepherd punched Zaeed and forces him to help save the factory workers. This unfortunately buys Vigo enough time to escape though it is a close call when one of Zaeed's bullets hits the soldier next to him. Zaeed is appalled that Vigo got away and almost opens fire on Shepherd when an explosions pins a large metal beam on top of him. Shepherd reassures Zaeed and saves him from burning to death. Zaeed is one of the squadmates to storm the Collector base beyond the Omega 4 relay and survive. After the mission Commander Shepherd is ordered back to Alliance space to face charges after accidentally killing 300,00 Batarian colonists. Because of this most of the squad including Zaeed leave the ship to avoid an Alliance interrogation.
Mass Effect 3
Zaeed continued his life as a bounty hunter and mercenary and was again asked by Cerberus for assistance. The negotiaons ended badly and Zaeed began a crusade to take any job that hamoered Cerberus operations. Not hard when Zaeed had killed 50 or so Cerberus operatives before even meeting Commander Shepherd. Zaeed appears on the Citadel after the attempted coup by Cerberus investigating Din Korlack the Volus ambassador who has ties to Cerberus. Din has a bounty on his head and Zaeed signed on at the last minute when he heard about his ties to Cerberus. Din kept a radio transmitter in his office which was found by Commander Shepherd. Shepherd guided Din into dropping his name so Zaeed would learn he was making a mistake. Zaeed then proceeded to kill every mercenary in the room and saved Din's life. Din was sought after by Cerberus because he knew the location of their next target, a Turian coloney names Aethas. Cerberus wanted it for their shipyards. Shepherd and Zaeed where able to convince Din into giving the name of the colony as well as supplying the Volus bombing fleet to the war effort. Zaeed then joined in as well and contacted some old colleagues to join the war effort.
Zaeed is next seen when Shepherd is on the Citadel on shore leave after the incident with CAT6 and the Shepherd clone. Zaeed is invited to a party at Shepherd's new apartment and spends his time hanging with the more battle ready members of the Normandy crew like Javik, Wrex, Garrus, and Grunt. Zaeed will either talk about ways to booby trap the apartment with Garrus or drunkenly hit on Samara depending on the mood of the party. Afterwords Zaeed will go to Castle Arcade and try to win a doll out of the claw machine for a child. When Zaeed cannot win the game he blames the maker of the game and intends on finding him afterward. Shepherd will then hangout with Zaeed. Zaeed can then be called upon at the Armax Arsenal Arena.
Once the battle for Earth is underway Zaeed places an order in preparation for ammo, whiskey, guns, and a repair kit for is beloved rifle Jessie. Zaeed will have one last talk with Shepherd before the final push towards the Citadel beam saying this doesn't feel like a ground war since the opponents are taller than the skyscrapers. Zaeed ends the conversation with "Lets gut the bastards."
Powers and Abilities
Zaeed is a normal human by Mass Effect standards but his skill, determination, and will to live make him a devastating force to be reckoned with. Zaeed's typical load out is an assualt rifle and sniper rifle and he is partial to Inferno grenades. Zaeed's personal weapon is a discontinued Avenger assault rifle names Jessie. Zaeed is skilled in hand to hand combat and knife fighting and throwing.
Mass Effect 2 - Zaeed can instead gain loyalty to Shepherd by having him kill Vigo though at the cost of the Refinery workers. If the workers are saved and Zaeed is not convinced of this goal he may die during the Suicide mission though he stills has a chance of surviving it. Alternativley is Shepherd completes the sucidie mission and has 2 party members besides Zaeed he can leave him to die under the metal beam during the loyalty mission.
Mass Effect 3 - Zaeed can due protecting Din Korlack if he was not loyal to Shepherd in the previous game.