Patrick Stewart has recounted in several interviews that his character was (he was told by Gene Roddenberry) based very firmly on Horatio Hornblower.
"The other thing that Gene [Roddenberry] said to me at a meeting was, because I said to him "Come on, come on, I'm new to all of this. Help me. Tell me. Give me leads, pointers, something that I can grab hold of" and he said "Tomorrow I'm going to send round to your home, copies of all the Horatio Hornblower stories. That's all you need to know". And he based Picard on that character in those Forster novels. And so I read two or three of them and I think I got what he was talking about. A combination of adventurer and moral uprightness and ambition and love of his job, too."
As regards Nicholas Meyer, apparently he 'stumbled' onto the idea that Star Trek (in this case with Kirk at the helm) was basically just a set of Hornblower novels in space. When he mentioned it to Harve Bennett and William Shatner, this was met with significant notes of approval.
Q: How did you get to direct “Star Trek II?”
A: I was hired to direct it before there was actually a script. I had my friend Karen Moore, who was a childhood friend of mine, tell me when she was an executive at Paramount that I should go and meet with Harve Bennett (who was in charge of producing the next “Star Trek” movie), which I did. That was really sort of love at first sight. I just thought he was sensational. I didn’t really know what “Star Trek” was. I might not have hung around to find out, I suppose, if I hadn’t liked him so much.
Then when we started talking about it back and forth and he showed me some of the episodes (from the TV series created by Gene Roddenberry) and the first movie (directed by Robert Wise) and, particularly, I think when I landed on my Hornblower analogy, which Gene Roddenberry, I think, arguably had landed on before me, then I got really stoked on the idea so they were making my directing deal predicated on this incoming script. I was in place to do that, I think, before there was what they considered a finished script — and, in reality, what they had in five different scripts.
Q & A WITH WRITER-DIRECTOR NICHOLAS MEYER
After they spoke, Meyer saw the connection between "Star Trek" and
C.S. Forrester's novels about the English sea captain Horatio
Hornblower. Having enjoyed those books as a teenager, Meyer understood
"Star Trek" was really just Hornblower in space.
When he shared his Hornblower idea with William Shatner, Meyer
recalled, Captain Kirk knew exactly what he meant.
Shatner (to Meyer): "Oh well, that's what Gene always said it was."
Nicholas Meyer recalls the making of 'Star Trek' II, IV, VI