When you think of sidekicks, Robin the Boy Wonder has to be one of the first to pop in your mind.
I don't even think the word "sidekick" joined the cultural lexicon until Dick Grayson made his first appearance waaaaaaay back in 1940 (Batman No. 1).
Robin, appropriately enough, ranked No. 2 behind Ed "Heeeeere's Johnny!" McMahon in Entertainment Weekly's list of the "50 Greatest Sidekicks." (For the full list and EW's ode to each sidekick that spans all parts of pop culture, go here, a link that starts with No. 25.)
Being a sidekick is a tough gig, especially if you're Batman's partner in crimefighting. EW calls Robin "the most iconic comic-book No. 2 of all time" and "a perfect No. 2 template." It's equally true Robin epitomizes being a sidekick: "letting No. 1 get all the glory."
Sidekicks are the butt of a lot of pop culture jokes. But at least in the comics, sidekicks serve some important purposes. Initially, Robin's creation gave Batman someone with whom to converse and a person with whom to discuss and dissect cases; this avoided readers enduring countless thought bubbles. Obviously, sidekicks have their partner's back in a fist fight.
Sidekicks also bear the responsibility and honor of taking over from their mentor. We've seen this more and more over the last 20 years, most notably Kid Flash (Wally West) becoming the second Flash after Barry Allen died. Even now, James Buchanan "Bucky" Barnes — better known as Bucky in World War II — has assumed the mantle of Captain America after the untimely assassination of Steve Rogers. And from what I've read online from Cap readers, the Sentinel of Liberty stories haven't been this good in ages.
In the Batman universe, even the sidekicks get replaced.
After flying mostly solo as Robin the Teen Wonder and then leading The Teen Titans, a young adult Dick Grayson finally decided he'd had enough of being thought of as "Batman's former sidekick." He quit being Robin and became Nightwing, a guise that ironically is tailored after the Dark Knight himself.
Soon afterwards, Batman took an unruly Jason Todd under his wings after the juvenile delinquent tried to steal the wheels off the Batmobile. Robin II was rebellious and insubordinate and most often, hard to like. Five years of real time later, he was brutally beaten by The Joker and blown up in a warehouse explosion Batman was helpless to stop — Robin II's fate of being killed off made by readers in phone poll. (Jason was later resurrected and remains a DC character. For his detailed, complicated history, go to this Wikipedia link.)
Following years of Batman being written as a loner, sometimes borderline psychotic, Tim Drake determined Bruce Wayne's and Dick's secret identities and flatly told Bruce that Batman needed a Robin to keep the Dark Knight better balanced — an homage to the rationale behind Robin's creation in the first place. Batman/Bruce relunctantly agreed to train Tim to be the third Robin, only allowing him to patrol the streets when Batman deemed he was ready.
Robin III is a good mix of the previous incarnations — an independent soul who is loyal to Batman, like a younger brother to Nightwing (who himself has found a way to positively relate to Bruce Wayne again), yet isn't afraid to question Batman's behavior or plans.
Creators also were able to differentiate Tim Drake from his predecessors by giving him a darker version of the costume the first two Robins wore (now under its second variation) and his own version of the Batmobile, the Redbird. After Tim's father was murdered at his own home, Bruce Wayne adopted the teen as his son (Dick and Jason were his wards).
There have even been a couple girls who have been Robin. In the alternative what-if future tale "The Dark Knight Returns," Carrie Kelly creates a spot-on version of Dick Grayson's outfit to be Batman's partner. Within the last three or four years, Tim Drake quit as Robin because of the stress it was putting among his father, Bruce and himself. Stephanie Brown, the villain-turned hero Spoiler, was briefly Robin IV, only to be killed during a gang war. Tim mourned the death of his one-time girlfriend, but soon rejoined Batman.
Over the years, we've witnessed the Batman-Robin relationship evolve from the chummy relationship between Bruce Wayne and his ward Dick Grayson through the 1960s to one of angst in the 1970s, eventually leading to hard feelings. The once distant relationship has since become a comfortable, yet respectful, agree-to-disagree dynamic.
There's been a third Robin (Tim Drake) introduced who later even got his own series after an arguably mentally disturbed Batman dealt with the pressure of losing a young, impetuous partner (Robin II) at the hands of his worst enemy.
There are more changes on the horizon for Batman and Robin. Bruce Wayne has learned he fathered a love child by Talia al Ghul, daughter of his longtime foe, Ra's al Ghul. Damian al Ghul came up with his own Robin Hood take on the latest Robin suit; his demand to be recognized as the rightful heir to Bruce Wayne makes Jason Todd's reckless attitude look almost tame. The tension between Damian and Tim Drake has led to a fight in the bowels of the Batcave. Where Damian's place in the Batman universe will be is anybody's guess.
Now, the "Batman R.I.P" story is coming to a close. With the upcoming "Battle for the Cowl" stories, it seems obvious Dick Grayson — as he did briefly during the "Prodigal" storyline — will take over the Mantle of the Bat. Probably permanently. It's doubtful Robin III is going anywhere, but it seems quite likely Jason Todd (resurrected as a vicious vigilante Red Hood) and Damian al Ghul will play important roles in the Batman family.
As you've just read, Robin's presence (no matter who is in the tights) has certainly put the "dynamic" in the Dynamic Duo. And that's the way it should be, because many times it's the so-called sidekick that makes the partnership so intriguing.