Prime (rank)
"Prime" is an Autobot rank of highest distinction in many Transformers continuities. It appears to be bestowed only on those that carry either the Creation Matrix or Matrix of Leadership.
Marvel Comic continuity
The idea of Prime being a title/rank has its fullest expression here. A direct lineage of Creation Matrix bearers is established, each taking on a derivation of the name of their god Primus: Prima, Prime Nova, Sentinel Prime, Optimus Prime, and Rodimus Prime.
Of note is that the name Prime has no real necessary relation to Autobot leadership here. Optimus Prime becomes a Prime long before he becomes the overall Autobot Commander. Rather, Prime is a religious title (as the Creation Matrix is a religious artifact: a relic of their god). The closest human analogue to a Prime might be the Pope.
Cartoon continuity
The evidence for "Prime" being a rank here is weaker than elsewhere but the case can still be made. Though many Matrix-Bearers are seen, and all are by definition Autobot Leaders, only three are ever named; 2 Primes, 1 not: Alpha Trion, Optimus Prime, and Rodimus Prime. Without knowing any other names it is hard to make a concrete case here for "Prime" being a title given only to Matrix-Bearers.
Still, Optimus Prime named Rodimus, and it's hard to imagine him egotistically dubbing his successor with a derivation of his own name if "Prime" weren't traditional.
It is of note though that if it were, then "Prime" in this continuity would be a military/political title (since it is the Matrix of Leadership), rather than the religious title of the Marvel Comics.
Japanese equivalent: Convoy
(Note: Not all Convoys are Primes. If you can lead ant-droids to a picnic, you're a Convoy in Japan.)
