Leland was a wall-street wizard and got the nickname Owl by his peers. The IRS started snooping and revealed his ties to the underworld. Depressed, he took a serum that gave him the ability of flight. He has had several clashes with Daredevil, Spider-Man, Black Widow, and even Doctor Octopus. Through the years, the serum has caused him to mutate further. He has recently resurfaced to take revenge on Daredevil. The Hood later seemingly killed Owl in order to gain respect among the figures of New York's criminal underworld and steal Deathlok from him.
Later, it turns out Owl survived the attack, as he is under police custody, but gets freed by Kingpin's henchmen shortly - in return Wilson Fisk wants Owlsley's services in order to distract Daredevil and takeover The Hand. That leads to capture of Dakota North, who Owl plans to torture, but his plot gets ruined once again by Daredevil, who shows no mercy to his long time nemesis - he cuts Owl's arms and legs with a sword, very likely crippling him by doing so. This also lead to the beginning of Shadowland event.
Further fate of Owl has yet to be revealed.
The Owl was created by Stan Lee and Joe Orlando in 1965 and first appeared in Daredevil #3.
Powers & Abilities
Flight, enhanced sight, hearing, and smell, above-average strength and speed, razor-sharp claws, and mild healing abilities.
It's a common misconception that Owl is a mutant, but he is a mutate who got his powers from experimenting on himself.
Earth 295: Age of Apocalypse
In the Age of Apocalypse reality, Owl was a member of the Marauders (Human terrorists enhanced by Apocalypse), along with teammates Arcade, Kingpin, and Red (aka Norman Osborn). The four villains were sent by Apocalypse to destroy the land of Wakanda. Though they were able to murder Black Panther and destroy much of the land, Owl's life was cut short by Hawkeye, who blew him up with an explosive missile.
It is assumed that this Owl had the same powers as the one in the regular Marvel Universe (Earth-616). He also was equipped with wrist weapons and "air-steppers"; boot attachments that allowed him near-flight.