That's a much harder question than you might think, because Berry Gordy originally started Tamla Records (and Rayber Records) before Motown, and he also originally only distributed records locally on Tamla and Motown, while licensing the records to larger labels (such as Chess) for national distribution. Gordy had been working with numerous artists, so we need to determine which of those artists ended up on a Gordy-owned label. Many of those artists had already had records on other labels (such as the Miracles' "Got a Job" on End Records, which came out in early 1958 and for which Gordy received less than $4 despite it reaching the top 10 on the R&B charts).
But the first artist recorded by Gordy and released on a Berry Gordy-owned label is uncertain. It's generally accepted that the first Motown record was Tamla 101, "Come to Me" by Marv Johnson, released in early (perhaps January) 1959, which was then nationally distributed by United Artists and became a hit.
BUT it's not really possible to know if Tamla 101 actually was recorded before Rayber 1001, "I Can't Concentrate" by Wade Jones (with its B-side, "Insane", written by Gordy and a young Smokey Robinson), which both seemed to have been recorded in January 1959. And, since this was the only single on Rayber, it's not possible to know if Gordy even considered this song or artist to be in the Tamla/Motown lineage (perhaps he just forgot about it). (NOTE: "Rayber" got its name from Gordy's wife Raynoma, known as "Miss Ray", and "Ber"ry Gordy himself. Maybe he wiped it because of his divorce from Miss Ray shortly thereafter.)
So the "official" answer is Marv Johnson (on Tamla), and the "official" date is January 1959.
The first single on Motown proper was "Bad Girl" by the Miracles in September of that year (Motown G1), after their other contracts had lapsed; it had been released by Chess in August and became a hit (the first Miracles record to reach the Billboard Top 100), but Chess failed to pay royalties promptly, leading to Robinson pushing Gordy to stop licensing records. And Gordy did exactly that, starting a new numbering sequence for Motown (M-1000) and using that label for the records he was distributing himself, while moving the Miracles over to Tamla with their next single.
The entire structure became increasingly complicated, but when Barrett Strong's recording of Gordy's "Money (That's What I Want)" (originally issued as Tamla 54027, which meant that it was supposed to be the 7th record issued on Tamla in the revised sequence (but was actually the 8th due to a numbering error), in August 1959) was then licensed by Gordy to his older sister Gwen's "Anna" label (also distributed by Chess) and became a huge hit (reaching the top 25 on Billboard and eventually being covered by just about everyone, including the Beatles), Gordy had the money to distribute that new Motown sequence. And everything is much clearer after that.
But to reiterate, if your question is taken to mean Berry Gordy's labels, the answer is Marv Johnson; if your question is taken to mean just Motown proper, the answer is The Miracles.
https://en.m.wikipedia.org/wiki/Motown_singles_discography
https://motownjunkies.co.uk/2009/10/05/o/
https://motownjunkies.co.uk/2009/10/05/00/
https://motownjunkies.co.uk/2009/10/05/1/
https://en.m.wikipedia.org/wiki/Come_to_Me_(Marv_Johnson_song)
https://motownjunkies.co.uk/2009/10/06/15/
https://motownjunkies.co.uk/2009/10/06/19/
