Larry is one of several random encounters throughout the game. He can be recruited as a weapons vendor and sent to a player settlement. When asked about his story he says "People want something, Smilling Larry find it and bring it to them, all Commonwealth know me".
ps4It is possible to have Larry at your settlement, but it is very very hard, spot him, kill his mercenaries and brahmin, lure him to the nearest settlement with 30 settlers, then go sleep 24h to make him friendly, use "work for me" dialog option, and go fast travel away, then fast travel back and assign him to the weapons emporium.[verification overdue]
If Larry disappears after being sent to a settlement, he may end up in the "Quick test cell" limbo which is a very small test room, with other random NPC such as Scribe, Ness, Mr. Gutsy, etc. Ness will be hostile and may possibly kill any non-essential NPC. If he disappears, use player.moveto 2f2a7 to find him and other NPC.[platforms tag needed][verification overdue]
pcxboxoneps4 Some Level 4 Merchants won't travel to or stay at your settlement after being assigned there. Solution: after the merchant has been assigned, disable them and any other travelling companions they spawned with, such as accompanying mercenaries ("prid [ref id]", "disable"); fast travel away from the area they spawned in; then walk, don't fast travel, back to that exact same area and a different random encounter should occur, such as wild mongrels or synths; if so, re-enable the merchant ("prid [ref id]", "enable"); fast travel to your settlement; and finally, move the merchant to you ("prid [ref id]", "moveto player"). Now the merchant should stay put.[verification overdue]
pcps4 It is likely that Larry will never appear at a settlement once hired.[verification overdue]
It is possible to assign him to tasks by using the console: target him with prid 0002f2a7, enter setpv bCommandable 1, setpv bAllowMove 1 and setpv bAllowCaravan 1, then fast travel to a remote location and return, after that you will be able to command him using the workshop menu.
Another solution is to head to the settlement where he is wanted, type prid 0002f2a7 in the console to select Larry, then disable, enable, and finally moveto player.[platforms tag needed][verification overdue]
xboxoneps4 It is possible to encounter Larry in the wild as a random encounter after recruited and put to work. It appears the game still counts him as a settler at the chosen location and remains assigned to the work he was given with the same caps and inventory as he would have at the settlement.
Though he cannot be recruited a second time it is unknown if he will eventually return to the chosen settlement after randomly encountered a second time. [verification overdue]