A Birthday is the anniversary of an individuals birth. In just about every reality the occasion is celebrated by the individual in question along with their loved ones. Common traditions associated with birthdays include holding a party or a gathering, the giving of presents to the one who's birthday it is, and the presentation and consumption of a birthday cake.

Known Prime Zone Birthdays

Current Timeline

Sonic the Hedgehog's birthday was comemorated with a surprise birthday party held by his friends, which was interuppted when the Time Eater appeared and distorted time and space. After teaming up with his younger self from the past, he eventually defeated the monster and restored reality-and the party-to normal. This event was also believed to have occurred during the timeline briefly created by the second Genesis Wave. (VG: SG, StH: #250)

Pre-Super Genesis Wave Timeline

Sonic celebrated his 15th birthday in 3235 by waking in the early hours and stuffing himself with chili dogs as an early birthday gift to himself. A year later, Sonic returned with Tails from their hunt for Ixis Naugus just in time for the hero to celebrate his 16th birthday. The year after that, Sonic celebrated what was presumably his 17th birthday (his actual age up for debate due to his time in space), only for the party to be crashed by Bean and Bark and later Croctobot. A few days later, another party was organised to make up for the previous party being ruined, although it ended up being postponed several times due to Sonic himself constantly missing it. (StH: #11, #68, #160, #161, #167)

Knuckles the Echidna celebrated his own 16th birthday not long after Sonic's: his friends the Chaotix organised a surprise party for him. (KtE: #28)

In 3235, Princess Sally celebrated her birthday; Sonic brought a Mobian Needle Bird named Thorny back to Knothole to give her as a present, but suspected the bird of being part of a Robotnik booby-trap. (StH: #9)

In 3224, Miles "Tails" Prower was born, his birth witnessed by his future surrogate brother Sonic. (SSS: #9)

In 3236, Sally and her mother visited the grave of Sally's late mentor Julayla Chipmunk, on the deceased's birthday. (StH: #120)

Known Birthdays in Other Zones

In the Another Time, Another Place reality, this zones version of Sonic the Hedgehog also had his surprise birthday party interrupted by the Time Eater. (StH: #230)

On Earth 20XX, the whole of Mega City turned out to celebrate Mega Man's 1st birthday (or more specifically, the one year anniversary of his creation). The occasion was interrupted when the blue bombers estranged brother Proto Man (at this point going by the name "Break Man") attacked the crowd. The two battled eachother until the second Genesis Wave enveloped their world. (FCBD: #7)

In the Sonic X Zone, a young Chris Thorndyke was treated to a camp-out birthday party with his friends after being disappointed that his parents wouldn't be able to make it for the occasion. In the present day, Chris' birthday was celebrated in spectacular fasion as his parents arranged for him and his friends (including Sonic and company) to attend the World's Fair in Paris, France. (SX: #5, #7, #8, #9)