>>5839114He's one of the Primes. That is to say, in IDW there's a lineage of Primes, but most of them are considered to be false Primes.
The original Primes were tribal leaders, thirteen of them, but they either died or left Cybertron. After all of them were gone, one of the tribe of Prima by the name of Nova Major took on the title of Prime, and called himself Nova Prime. Eventually he left Cybertron, too, but he left behind the Matrix of Leadership, which is believed to be what makes a Prime, truly a Prime. Nominus Prime succeeded Nova Prime, but the Matrix was hidden, and he used a false Matrix instead. Nominus Prime was murdered, probably by Sentinel, who was working for the corrupt and oppressive Senate. Sentinel took the Matrix, although he realized it wasn't the real thing, and functioned as the Prime - although still in service to the Senate - until he, too, was killed, by Megatron.
Anyway, he was resurrected and this is his new form.
