What was Metra's 1st Train ever?

What was Metra's 1st train they ever ran?

If you're referring to Metra and only Metra, then it would be the earliest train that ran on the day the official management changeover from RTA to Metra. But if you're thinking the RTA too (since it was Metra's predecessor), then I'm guessing it would have been a train on one of the former MILW routes.

I mean both.

RI was the first line to be taken over by RTA.

If you want to go back further, the Milwaukee Road commuter service was funded by the NWSMTD in the early-mid-70's. While that wasn't the RTA, it still exists today under the RTA as far as I know.