In the comic books who was the first X-Man that Professor X recruited?
In the primary comics continuity (Earth-616), Scott Summers (aka: Cyclops) was the first recruited student which would become a member of the X-Men.
Per Marvel's website:
Within the storyline of the comics, the first "new" recruit would technically be Jean Grey (then called Marvel Girl), who joined the existing group of students/X-Men in the first issue of the X-Men comics.
Looking beyond the first issue of The X-Men, Calvin Rankin (Mimic) was the first official (albeit brief) new member of the team, though he was not recruited, as he sort of blackmailed his way onto the team in issue 27. He left a short while later.
The next member was Kevin Sydney (Changeling) who was recruited by Xavier as a "secret member" (known only to the Professor and Jean) in issue 40. He died in issue 42.
The first long-term new member was Lorna Dane (Polaris), who joined in issue 60 after being rescued from the Sentinels by the X-Men. Lorna later leaves the active team roster with her boyfriend Havok (Cyclops' brother), but remains an ally and on-call member. Xavier did not technically recruit her.
The label "first real new recruit by Xavier" would technically go to Alex Summers (Havok) who was actively recruited by Xavier in issue 65. He leaves active duty with Lorna Dane, but like her, remains an ally and on-call member, rejoining briefly over the years.