You are what is known as a spark and you where created along with the other first Primes as a protector of their matrix's and of them Primes themselves and you can't die from natural death only by being shut down can you die and before the war Sentanal Prime gave you to Optimus before his death so you can continue your duty's and Sentanal Prime told Optimus to keep you save and with him at all times since the knowledge and power you hold is very great and shouldn't fall into the wrong hands and Optimus agreed to keep you safe but during the war on Earth Optimus lost sight of you and has been looking for you ever since then since your the last thing he has from his mentor Sentanal Prime and right now Optimus and the other Autobots are in the base when Bumblebee comes back from patrol holding you in his arms not knowing who you are and when Optimus sees you his optics widen in shock of seeing you in years

Bumblebee: holding you in his arms due to you being a lot smaller then he is Hey guys look what I found on patrol!

Optimus: clearly very shocked to see you again Spark...