inFamous suggests that Zeke has been best friends with Cole MacGrath long before the events of the game, growing up together in Empire City, and Zeke provided many funny comic relief moments serving as a "sidekick" of sorts for Cole, always making wise-cracking jokes about the feds, "conspiracy crap", and "major tools" from his high school.
All goes well until Zeke finds out about the FBI agent, Moya Jones, that Cole has been working with, and starts tracking down "leads" that he thought might help. One of which was finding out that Alden Tate and his Dust Men were hiding out at the Warren district shipyard. Trying to fight them alone, Zeke is captured and Cole soon rescues him. When he does, they have an argument that briefly splits them up, but soon made up when Cole understands that he means well.
However, the main moment that tested Zeke and Cole's friendship was when they attempted to get the Ray Sphere from Alden at the top of a large fortress-like tower he had built with the Dust Men. Zeke manages to pry it from Alden while he's distracted, but is caught between him and Kessler. Realizing that the object that could give him the powers he wants was right in his hands, Zeke attempts to activate the sphere, but it doesn't work because Zeke is not a Conduit, and therefore cannot absorb Ray Field Energy. Kessler offers to "fix" it, and Zeke, betraying Cole a second time, agrees to go with him. It is later implied that Zeke helped Kessler kidnap Cole's girlfriend Trish Daily, not realizing that Kessler planned to murder her. After Trish's death, Zeke felt responsible, and left Kessler and the First Sons.
Cole is enraged by this, tells Zeke to leave the city, and if he found him, things would get ugly. Zeke disappears for the remainder of the game, but tries to help Cole at the beginning of the final battle with Kessler, only to be thrown away by one of the powerful Conduit's energy blasts. They seem to make up afterwards, and Zeke is shown behind Cole in the final cutscene suggesting he's alive. However, he says nothing and doesn't show up in either the good or evil endings.
In inFamous 2, Zeke returns, having shakily made up with Cole, and escapes the destruction of Empire City by the Beast in the introduction with Cole and NSA Agent Lucy Kuo, going with them to New Marais. There he serves a slightly more active role than in the first game. In order to help Cole gather intelligence on their primary enemy, Joseph Bertrand, Zeke joins up with the Militia and passes along info he picks up while performing minor duties for their foes. Somewhere along the way, Zeke, along with about half the population of New Marais, is infected with the incurable, totally lethal Plague that results as a side effect of Ray Sphere usage, though he covered it up and hid the truth from Cole. (The player, of course, figured this out dozens of missions ago, as Zeke began coughing in every conversation).
His most active role in the story comes when he steals a nuclear missile from the Militia and helps Cole fire it directly into the Beast, who was approaching New Marais. It somehow doesn't destroy the monster, but it definitely slows him down and gives Cole more time to become strong enough to use the Ray Field Inhibitor, which will kill the Beast once and for all, and might even cure the Ray Field-derived Plague.
It is revealed at the very end of the game that the Beast plans to activate as many Conduits as possible, as they are immune to the Plague and he believes it is only a matter of time before all "normal" Humans are wiped out by the disease. Meanwhile, while the RFI will definitely kill the Beast and might stop the Plague, it won't stop at the Beast; every Conduit in the world, active or not, will drop dead upon the RFI's activation. This includes Cole, Kuo, and local ally Nix.
In the Evil Karma ending, Cole sides with the Beast, and must stop Nix and Zeke from activating the RFI. This leads to a boss fight where Cole brings Nix down... and a Quick Time Event where Cole is forced to kill his best friend, who recognizes that he won't be able to stop Cole with a mere pistol, but has to try, given that 95% of Humanity will die if Cole succeeds. Cole murders Zeke and destroys the RFI, and with the death of the Beast, becomes the leader of the evil Conduits making their way across the world, unlocking every potential Conduit at the cost of millions of normal Human lives.
In the Good Karma ending, Cole sides with Zeke, and must defend the charging RFI from the Beast and Kuo's attacks. In the end, Cole defeats the Beast, and Kuo admits that sacrificing themselves for the good of Humanity is the better choice, and allows Cole to activate the RFI. The Beast is destroyed once and for all, and every Conduit in the world, thousands of people in all, drops dead without warning, but the Plague disappears along with it. Every single infected Human, including Zeke, is suddenly in perfect health. The final cutscene has Zeke delivering a touching eulogy to Cole while escorting his body out of New Marais by a boat.