Masked superheroes often keep their identity secret so they can live a normal life away from the capes and tights and keep their loved ones safe from villainous repercussions, though some heroes are better at it than others. Matt Murdock is a shining example as his costumed alter ego, Daredevil, has been revealed in the comics a number of times.
While Daredevil's identity in the comics is currently under wraps, there have been quite a few people who have discovered Murdock's secret over the years, from his closest friends and superhero allies to his worst enemies and even the general public, though he's almost always managed to lawyer things his way to put the cat back in the bag.
10 Dr. Van Eyck Deduced His identity & Then Died — Daredevil #9 (1965)
Matt Murdock's identity was revealed early in his crime-fighting career after he sought out the missing Dr. Van Eyck, who had pioneered an experimental operation that could restore sight to the blind.
Unfortunately, Van Eyck was being held captive by an oppressive government, and Daredevil was forced into action to stop plans to release a cloud of nuclear material. Dr. Van Eyck figured out that Matt Murdock and Daredevil were the same due to his physique, though he sacrificed himself to stop the release of the nuclear cloud before revealing his knowledge.
9 Unmasked & Exposed By Spider-Man — Daredevil #24 (1967)
One of Matt Murdock's closest superhero allies is Spider-Man, and the two have formed a close friendship over the years after they each deduced one another's identities before ultimately unmasking to each other during Spectacular Spider-Man's "The Death of Jean DeWolff" storyline.
However, Spider-Man had previously decided to confront Matt Murdock regarding his suspicions by sending a letter to his law office, which was read out loud by Karen Page in front of Foggy Nelson. Matt lied and posed as his twin brother "Mike" Murdock to throw his closest friends off the scent by making them think Mike was Daredevil, which became an ongoing cover.
8 Machinesmith Tracked Daredevil To Murdock's Apartment — Daredevil #51 (1969)
Starr Saxon was a brilliant robotics inventor who was hired to take out Daredevil using an android of his own creation that was able to track Daredevil using an advanced aroma detector keyed to Daredevil's body type.
Saxon tracked the results back to Murdock's apartment and discovered his costume and equipment, leading him to kidnap Karen Page in an attempt to get at Daredevil. Saxon escaped and returned as the new Mister Fear before his death led to his new artificial existence as Machinesmith, though he abandoned his vendetta against Daredevil.
7 Matt Murdock Revealed his Identity To Karen Page — Daredevil #57 (1969)
After Saxon discovered his secret identity, Daredevil decided to live his costumed life full time and faked the death of Matt Murdock in a plane crash, leaving Karen Page heartbroken as the loss of the man she loved. Following an attack by Karen Page's father Death's Head that led to his death, Daredevil decided to let Karen remove his mask and reveal himself as Matt Murdock.
This surprised Karen both with his secret identity and the fact that he had faked his death. though she had trouble accepting his dual lives and their relationship never seemed to recover. Karen was just the first of many girlfriends Matt would reveal his identity to over the years.
6 Put Together By A TV News Station — Daredevil #92 (1972)
A San Francisco TV station released a report that connected Matt Murdock and Daredevil's presence in San Francisco, along with their equally documented relationships with Black Widow that the news reporter used to claim that Matt Murdock and Daredevil were one and the same.
Murdock was able to throw off suspicion by having his ally Black Panther (who had recently deduced Murdock's identity) wear a Daredevil costume while Murdock arrived on the scene, explaining that his brother Mike Murdock had died and been replaced by a new Daredevil who had traveled to San Francisco to protect Matt on his late brother's behalf.
5 Purple Man Discovered His Secret — Daredevil #154 (1978)
Zebediah Killgrave/Purple Man has the unique ability to sway others to his will using his enhanced pheromones, and he faced off against Daredevil quite a few times during his villainous career as a costumed criminal, which allowed him to deduce that Daredevil was blind.
One of his final acts as a costumed villain before he became an evil hidden manipulator was to kidnap Daredevil and force him to fight controlled enemies for the life of his girlfriend, Heather Glenn. He taunted Daredevil with the knowledge of his secret identity, though disappeared after falling to his apparent death.
4 Karen Page Sold His Identity For Drugs — Daredevil #227 (1986)
Karen and Matt's relationship went through a number of hurdles after he revealed his identity, and she eventually left for L.A. to pursue a film career that resulted in her involvement with shady characters that turned her towards drugs and pornographic film roles. An addicted and desperate Karen Page then sold the only valuable information she had left, which was Daredevil's identity.
Wilson Fisk/Kingpin eventually purchased the information and set about killing everyone who had learned Daredevil's secret so that he alone could exploit the revelation that Murdock was the costumed crime-fighter. Kingpin systematically tore apart Murdock's civilian life and career and Daredevil's public opinion during the iconic "Born Again" storyline.
3 Leaked Using Ben Urich's Stolen Files — Daredevil #323 (1993)
Daily Bugle reporter Ben Urich had actually figured out Daredevil's secret identity earlier in Daredevil #164 through his own investigative methods, though he decided to keep the secret to himself as he felt Daredevil's role as protector of the city was more important than the story.
Unfortunately, his files were hacked by his assistant who leaked the revelation to the papers during the "Fall From Grace" storyline. While Murdock was able to disguise his place and discredit the report, he still faked his death and used a different name (Jack Batlin) and costume until he was ready to restore his secret identity using a double.
2 An FBI Agent Leaked Daredevil's Identity To The Press — Daredevil #32 (2002)
Kingpin's information on Daredevil's secret identity eventually leaked out of his inner circle among the underworld, which led to a failed coup by one of his underlings who felt Kingpin was weak for not using the information. FBI agents investigating Kingpin and the attempted coup also learned the information, which they were ordered to ignore so as to focus on the criminals.
However, one of the agents leaks the information to a local newspaper. Matt Murdock struggled to deny the claim, and at one point even publicly declared himself the new Kingpin, leading the FBI to arrest him. He was eventually able to clear his name and remove suspicion on his name thanks to help from Iron Fist, who was posing as Daredevil while Murdock was in prison.
1 Revealed His Identity In Court To Avoid Blackmail — Daredevil #36 (2014)
Kingpin had assembled further proof that Murdock was Daredevil after initially learning of his identity, and that information continued to plague Murdock as he soon found himself blackmailed by leaders of the Sons of the Serpent, who threatened to expose his identity if he didn't assist them with their legal troubles.
Murdock then revealed his own identity in court while on the stand, and fully embraced his new celebrity, though it cost him his ability to practice law in New York. Daredevil's struggles with his public identity were ended after Purple Man's powerful children used a power-enhancing machine to spread their influence across the planet to make everyone forget Daredevil's secret identity.