The name "Malodor" is a pun on his stink; "mal" means "bad" in French, and taking that with "odor" it comes out as "bad smell", which is appropriate for a skunk-themed Decepticon.
In flashbacks, a young Optimus Prime appears doing a training exercise. During it he transforms from robot to vehicle mode and back again, revealing that not only does his semi vehicle mode include a trailer, but that it also does not appear and disappear without explanation. Rather, it houses his arms in vehicle mode and telescopes into his shoulder cowlings in robot mode.