Timothy "Tim" Drake replaced Dick Grayson as Robin.
Tim Drake was the son of criminal Steven "Shifty" Drake, a thug for the crime lord Two-Face. He had very little respect for his father, and often had to fend for himself. Around the age of 10, Drake began to idolize Gotham City hero Batman and placed newspaper clippings on his wall. After Batman left a batarang behind at a crime scene, Drake found it and began using it himself.
Adventures as Robin
When his father double crossed Two-Face, Drake was left a note and a key to a Gotham City airport locker. This key was discovered by Two-Face's henchmen when they briefly kidnapped the youth. Two-Face flipped his coin, and decided to execute Drake, but Batman had rescued the boy. Soon after, they discovered that Drake's father was killed outside of Gotham. With no place to go, Bruce Wayne adopted Drake and began to mentor him under his tutelage as the second Robin.
Almost immediately, Drake began working in the field as Robin. One of his first acts was helping Batman thwart the Joker's attempt to kill Gothamites with his Joker Gas during a New Year's Eve celebration.
When Mr. Freeze began targeted assorted people in order to destroy people's hope, and went after Wayne's family, Mr. Freeze at first considered freezing Drake, the surrogate son, but ultimately decided to go after Alfred Pennyworth. Drake was left behind to watch over Alfred while Batman and Batgirl went after Mr. Freeze.
When the Scarecrow invented a gas that removes a person's fears, and Batman is turned into a man with a fearless attitude, Robin stops Batman out of fear his mentor is no longer afraid to kill. As the Dark Knight pretends contrition and offers to let Robin lead, Robin is nearly fooled, but sees through the façade just in time. When Batman nearly kills Scarecrow, Robin frees Batman with the antidote. With Batman back to normal, Robin is given Batman's praise for doing the right thing.
During one night of working solo, Robin came to the aid of a young girl with amnesia, developing a bit of a crush on the girl. She later proved to be a lost creation of Clayface in order to scout out Gotham for a return. Unfortunately, the girl had "forgotten" her purpose and continued to run. When Clayface reabsorbed the girl, Robin took her "murder" very hard and almost killed Clayface.
After fighting against pick-pockets and thieves, Robin asks why Nightwing left the Robin mantle. After hearing about his predecessor's last days as Robin, Robin and Nightwing learn about a night watchman at Wayne Enterprises. The two protégés of Batman leave when the Bat-signal comes on in the night sky to join Batman.
When Batman mysteriously went missing, Nightwing and Batgirl went to search for Wayne while Robin was left to defend Gotham by himself. When Superman arrived in Gotham, Robin teamed up the Man of Steel. With Robin as a guide, Superman was able to successfully masquerade as Batman for a time, and together, the duo discovered that Wayne was actually under Brainiac's mind-controlling nanites. They managed to save Wayne with Brainiac's destruction.
Later career as Robin
Sometime after Nightwing left to establish himself in another city, Robin was patrolling alone one night. Upon hearing a scream for help, Robin rushed to the aid of a lone woman being accosted by thugs when, in fact, he was falling into a trap set by the Joker and Harley Quinn. For the next three long weeks, at the old Arkham Asylum, Drake was mercilessly tortured with electro-shock and chemical injections. During the course of these torture sessions, Joker extracted the precious secrets entrusted to Robin. Not content with just destroying Drake's mind, the Clown Prince of Crime sought to further humiliate Batman. To this end, Joker transformed Drake into a crude, childlike version of himself: Drake's skin was bleached white, his hair dyed green, and his mouth was twisted into a grotesque, Joker-like grin. Because of the torture, disfigurement and brainwashing he endured for three weeks, he was also rendered unable to communicate in any way except with demented laughter.
Renamed "Joker Junior", aka "J.J.", Joker claimed the boy as his and Harley's 'new son', and planned on using Drake to destroy Batman. During a horrific battle, Joker gave Drake a gun to kill Batman with, although in a different version was the gun was fill with gas and to make him one of them. Drake laughed uncontrollably and fought with the choice of whether or not to kill, gas him in a different version, Batman. Fighting back and choosing to not kill, turn him into one of them, his mentor, Drake either used the bang gun or pushed the Joker into some chemical then electrocute himself which killed him instead, after which he completely broke down in Batgirl's arms. After these events, Batman and Batgirl buried the Joker deep beneath Arkham and Commissioner Gordon quickly covered up the incident and none of the details were ever made public. After the traumas that he suffered, Drake was shattered physically and psychologically, to which Dr. Leslie Thompkins spent a year treating him and a year later, Drake was finally recovered. After what had happened to Drake, Batman forbade Drake from donning the Robin costume ever again before Drake left, choosing to make the right decision for himself. Drake attempted several times to mend things with his former mentor only to fail. Despite his recovery, Drake would suffer horrible dreams for years.
Later in his life, and having completely gave up being a hero, Drake became a top-level communications engineer, a husband, and father of two. He apparently ended up regretting ever being Robin and had even less love for the suit than the Joker did. Despite his apparent hatred for his secret life during his teenage years, he still had a relationship with Barbara Gordon. On the other hand, Drake's relationship with Wayne was somewhat rockier, as he felt nothing but bitterness and scorn for his former mentor like with his life as Robin. It was later revealed, however, that much of his hatred for Wayne and his life as Robin was caused by another source entirely.
As it turned out, a DNA microchip with his tormentor's own memories and DNA was planted into Drake's spinal column during the time of his torture. As the years passed, the microchip activated, allowing the Joker's personality to emerge and take control of Drake, explaining his increased hatred for the Robin identity and Batman. The chip would also physically transform Drake into an exact replica of the Clown Prince of Crime. Using the host's communication engineering skills to take control of a satellite with a powerful weaponized laser on board, Joker went on a crime spree. Ultimately, however, the new Batman (Terry McGinnis) was able to destroy the microchip, freeing Drake of the Joker forever.
Having had all along been unaware of what had been seeded inside him, Drake was taken to the hospital for his injuries, and was visited by McGinnis, Barbara, and even Wayne. Barbara covered up Drake's involvement in the Joker's crimes, as he was technically innocent. As McGinnis took his leave to let Wayne and Drake catch up and both of them reconcile, Drake gave Terry the respect of being Batman, and he said that it meant a lot coming from him.
In the comics, Tim Drake was the third person to take the Robin identity while Jason Todd was the second holder of the title until he was killed by the Joker. Tim Drake's character in the animated series mixed certain elements of both comic-book characters together.
Like Jason, Tim was an orphan and a former thief living on the streets until he was taken in by Batman when his father disappeared after working for Two-Face. He also had a very rebellious streak that had a tendency to put him in trouble. Jason was also much more prone to be willing to endanger the lives of criminals if provoked and the animated Tim almost killed Clayface after his absorption of Annie. It is also worthy to note that, like Jason, the animated Tim's career as Robin was brought to a tragic and horrifying end by Joker, both involving torture (although Tim survived unlike Jason). Both also used at least one alias of Joker's as well: Jason used Joker's former Red Hood alias while Tim literally turned into Joker (although the reasons are different), and Jason willingly adopted his alias specifically to get revenge on Joker while Tim wasn't aware of Joker taking control of his body and mind. Parts of Animated Tim's tragedy were adapted in the Arkhamverse story of Jason, where instead of killing him, Joker tortures him in Arkham Asylum sending him insane, convincing him to become the Arkham Knight, though Jason was restored to sanity rather quickly and redeemed himself by rescuing Batman from Scarecrow. However, Tim did share a few qualities with his comic counterpart, in that he showed surprising knowledge and skill for detective work and was very adept at working with computers if need be.