The billionaire activist investor, in addition to mopping the floor with his hedge fund titan frenemy over their disagreement on Herbalife, was the first of the two to make it to Twitter, pushing out his first official tweet Thursday.
(Read More: Icahn, Ackman in Epic Showdown of Billionaires)
Here's Icahn's first, and thus far only, tweet.
Icahn remains in a pitched battle to prevent Michael Dell from keeping the computer maker from going private.
To date, Ackman, the head of Pershing Square Capital, has yet to show his face on the social networking site and its 140-character signature communication style.
As you may remember, the two famously battled on CNBC back in January.
Icahn's move comes the same week as another hedge funder, Doug Kass, became a Twitter quitter after announcing he was leaving the site due to "haters" who have pilloried him over his short market calls.
(Read More: Twitter Quitter: Kass Says He's Done With 'Haters')
Icahn knows a lot about haters, but nonetheless has amassed 4,215 followers so far.
Warren Buffett joined the site back on May 2, but has been a Twitter slacker, sending out only two messages, both on his initial day aboard.
Pope Francis has sent 67 tweets since joining March 17.
—By CNBC's Jeff Cox. Follow him
@JeffCoxCNBCcom on Twitter.