Major Story Arcs
Sparrow, the Grey Raven's sidekick, fights alongside him and Blaze in World War II, and then for three years in Chicago as they start C.O.W.L., the superhero union.
Eventually, under mysterious circumstances, the Dart (Blaze's brother) hurts Sparrow in 1955, and he drops out of sight. (This is explained in somewhat more detail in the movie, see below.) For equally mysterious reasons having to do with that battle, Sparrow and the Grey Raven (Geoffrey Warner) no longer get along, to the extent that Warner wants to cut him from his memoirs about the union.
Sparrow eventually comes back as a dark, hooded figure (similar to his identity as Wraith in the movie), and beats on a couple of thugs who saw the murder of John Pierce, forcing them to admit to what they saw. He is now quite vicious, willing to torture to get results.
Later, Chicago police detective Hewitt meets up with him and tells him that the case against Arclight (who killed Pierce) has fallen through, but that Warner doesn't know that Sparrow has been helping her with her investigation all along.
The series was canceled prematurely at this point, but presumably Sparrow was going to continue to play a part in bringing down the corrupt reign of Geoffrey Warner.
Sparrow is a skilled hand to hand combatant. This is mostly seen in the movie, but also alluded to in the comics. The movie says that Sparrow is a master of eight martial arts.
References to Other Characters
Sparrow, like other members of C.O.W.L., is obviously inspired by, and a reference to, classic heroes. In Sparrow's case, he is based partly on classic sidekicks like Bucky and Robin, both in their original forms as well as to later phases as Winter Soldier and Red Hood.
Sparrow appears in the movie The League, made before the comic by the same creators. He is more of the main character in the movie, and his backstory is much more fleshed out.
The League, the superhero union, is founded by the Grey Raven, Sparrow, and Blaze in the 1940s. At some point, one of the League's archenemies, the Dart, traumatically injures Sparrow, and he drops out of sight. Sparrow is said to have let the Dart escape, and to a degree seems shamed by the experience.
Seventeen years later, the Grey Raven (Geoffrey Warner) is planning on making the League a national union, but the Dart has resurfaced and is killing former villains. When an interviewer asks about Sparrow, Warner doesn't want to talk about him.
Sparrow, now missing an eye and calling himself Wraith, starts investigating. He gets into a confrontation with some League members and cops, and beats up Eclipse. He meets with Warner, and explains how he wants to get the Dart for what he did to him. Warner wants him to drop it, but Sparrow takes Warner's files.
Remembering a scrap of paper he found in a dead villain's hand, he goes back to the death scene and finds a note on the back of a poster. He follows the clue to another villain's hideout. The villain, Lennin, tells Sparrow that Warner is behind it all, and that Warner killed the Dart years ago for what he did to Sparrow. Eclipse and another League member break in, and they all fight. Eclipse's power goes wild, and Sparrow is only saved by the appearance of Blaze and his forcefield. Blaze says they miss having him on the team, but Sparrow doesn't want to be part of it any more.
Sparrow confronts Warner, who basically admits to what Lennin said. He says he did it because the League members don't know what else to do, and need to go national so they have a mission again.
Sparrow finds the one remaining villain, and hides him away, and tricks Blaze into showing up. He has realized that Blaze is really the one pretending to be the Dart, using his power ring (although he is working for Warner in doing so). They fight, and Blaze clearly has him outmatched, but he feels to guilty to kill Sparrow, and Sparrow takes advantage of his weakness to knock him out and deliver him to justice.