The 31-year-old has signed an 18-month contract with the Hammers to end a miserable spell at Liverpool.
Cole's talent had long been talked about even during his days in the West Ham academy, and after signing professional terms in 1998 he became a firm fans' favourite before leaving for Chelsea in 2003 after the east London club were relegated from the Premier League.
The England international went on to win eight major trophies - including three Premier League titles - with the Blues, but is now ready for the next chapter in his career after returning to where it all began.
"It is great to be back where I started and very surreal, walking out on pitches where I played when I was at under-13s," said Cole, who could make his second debut in Saturday's FA Cup third-round tie against Manchester United at Upton Park.
"It is weird, but I am happy, my family is happy and we are looking forward to it.
"For me, this season has been bad because there has not been a lot of playing time at Liverpool.
"The manager (Sam Allardyce) wants me to come here and play, I need to get games to come back up to fitness and match speed.
"I am buzzing to play and make my debut again."