The 32-year-old made 112 appearances for Boro, who he joined from West Ham in the summer of 2017 for a reported £5million fee (BBC Sport).
Randolph was previously at the East London club for two seasons, after being snapped up on a free transfer in July 2015 after leaving Birmingham City, and made 42 appearances in claret and blue (Transfermarkt).
The Republic of Ireland stopper's time at Boro was particularly fruitful as he won Player of the Year last season, was named in the Championship Team of the Year, and also made the club's Team of the Decade.
However, injuries have restricted Randolph's appearances this season for Boro as academy graduate Aynsley Pears stepped up into the goalkeeping role and has been doing well.
West Ham, meanwhile, were in the market for a new keeper this month, with Lukasz Fabianski recently returning to the side after injury and question marks over the performances of deputies Roberto and David Martin.
On Wednesday, both clubs confirmed that Randolph had rejoined the London Stadium side on a three-and-a-half-year contract, for a reported fee of around £4million (BBC Sport).
Here is what some West Ham fans have been saying on social media:
We are pleased to confirm the signing of a player that was deemed not good enough, to join the manager we also previously deemed not good enough. He will immediately slot straight into the line up for the massage bed, good luck Darren.— Wᴇsᴛ Hᴀᴍ Sᴏᴄɪᴀʟ (@WestHamSocial) 15 January 2020
Can I just say George it’s not negativity it’s just we are fed up with being mugged off— wickford willy (@davidmorris237) 15 January 2020
If he’s still injured I’m going to hunt you down— West Ham Transfers (@westhamtransfer) 15 January 2020
So we have brought in a keeper who hasn't played for months due to injury to cover our injured keepers. Clever move that. I have to ask, in what way do you think this is a good signing. We are the worst run club in the PL. Its actually embarrassing having the owners we have.— William Field (@wilfield71) 15 January 2020
Embarrassing! Next Level you say?— Carys Ann (@CarysAnnT) 15 January 2020
Talk about adding fuel to the fire. This signing will do just that. If anyone still believes the club has any ambition then I'm feeling sorry for you. It's ok to be loyal I respect that. But my loyalty is to the club not the owners who are merely custodians of the club.— William Field (@wilfield71) 15 January 2020
I doubt a single West Ham supporter is pleased about this. He was worse than Adrian, who we let go for nothing. Wasn't good enough 2 years ago. Presumably he was cheap as payments from Boro outstanding. The club deserves to be relegated: the supporters don't.— Paul Anderson (@PaulAndersonNE6) 15 January 2020
Signing a 32 year old injured goalkeeper on a 3.5 year deal to backup our injured 34 year old goalkeeper because our two 33 year old backup goalkeepers have been deemed not good enough.— Rob G (@rghammer6) 15 January 2020
Peak West Ham.
Joke of a club. I despair— Sx Ⓥ (@TheSteveDay) 15 January 2020
My club is a joke— thomas brown (@Brown24thomas) 15 January 2020
The only way im looking at it is, if it means Roberto never has to play for us ever again ... Swings and roundabouts— Dean Marsh™ (@deanrmarsh) 15 January 2020
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