Alright... this is a place where 3e and 4e style are very different.But they may fight him...
In 3e, there was a certain assumption that an NPC must be at least THIS combat worthy in order to be THAT good at picking locks. So if you wanted an NPC with a +20 Open Locks modifier, you could reverse engineer and determine how powerful he was in battle. You'd reason that he might be an "Expert" NPC class, that he might have a starting 15 Dexterity, that he might have the Skill Focus feat in Open Lock, and you'd conclude that he needs about 13 ranks in Open Lock plus his adjusted dexterity of 18 and his feat. So you'd make him a level 10 expert.
Of course the better you got at learning the details of the system, the more you could vary. For example, discovering some other feat that gave an untyped +2 bonus to Open Lock would free you to reduce his level by 2. Of course, that would lower his ability score bonuses from levelling up, so you'd really need to reduce by 1... and you'd work out all the details and get the outcome that you wanted. And if you didn't like how combat ready this guy became because of the high numbers of level in Expert, you'd learn tricks like sabotaging his constitution to ruin his hit points. Or you'd go off road with the system into the wilds of the uncharted, and give miscellaneous bonuses and penalties for half defined reasons in order to get everything to match what you wanted.
In 4e, things aren't interconnected like that. If you want someone to have a +20 bonus on checks to open locks, just say that he's got that bonus. Or don't bother- just declare that this NPC is "really darn good" at opening locks, and leave it at that. If you want this NPC to be combat effective to a certain degree, just make him so. If you want him to be incompetent in battle, just say so.
Pick the outcome you want, and make it happen. The system doesn't use the same organic process as 3e. Just do what you want.
Of if you like, tell people online what you want, and they'll make it for you for fun.