Brendan Gleeson plays a vintage Gibson

[Jim Garber]

It is definitely an old Gibson probably from the teens. You can tell because he spends a bit of time tuning it. He almost gets it there, too. I wish they met him play a bit longer.

[Richard500]

From Jack Benny through the Smothers, Steve Martin and hundreds more, the standup protocol is play no more than a few bars, even if one can. Sometimes an instrument is just a prop.

[Dan in NH]

I was thinking as I was watching “Who wouldn’t tune BEFORE coming out on stage?” Well, no one. So then the tuning must be an affectation, something to give him time to tell scripted jokes between strums.

Ok, and Henny Youngman.

[Mainer73]

He CAN play though. He's been a fiddler for a long time but seems to be favoring mando lately.

[Jill McAuley]

Brendan Gleeson keeps some pretty good company when it comes to playing tunes - I've seen clips of him playing with John Carty on FB and here he is playing with Mike McGoldrick:

[Mando Esq]

Does anyone recognize the tune he started to play?

[Charlie Bernstein]

I was thinking as I was watching “Who wouldn’t tune BEFORE coming out on stage?” . . .

He probably did. Seems like you just have to tune these things constantly.

[JEStanek]

That was fantastic and it struck me as great pub humor. It also struck me as intentional with the tuning as part of the bit and when given the chance a device to really blow your mind when he actually plays quite well, as Jill showed us above.

That was a riot. Also, ho weird to see Colin out of the Penguin suit from Batman.

Jamie

[Mainer73]

Does anyone recognize the tune he started to play?

Chief O'Neill's Hornpipe

[Mando Esq]

Chief O'Neill's Hornpipe

Much appreciated!

[Dan in NH]

The joke is mandolin players spend half their time tuning and half their time playing out of tune.

[seankeegan]

Mr. Mercedes, season 3 episode 3, ends with a lovely mandolin/fiddle duet of Brendan with Dylan Foley (fiddle player with the band 'The Yanks, all Ireland senior fiddle winner). Dylan also features in the episode, playing fiddle in the background of a pub scene.

[Bren]

Chief O'Neill's Hornpipe

One of the few tunes Barney McKenna would play on mandolin in concert back when you didn't hear mandolin so much in Irish groups.

[mandocrucian]

I was thinking as I was watching “Who wouldn’t tune BEFORE coming out on stage?” Well, no one. So then the tuning must be an affectation, something to give him time to tell scripted jokes between strums.

How do you know that the air conditioning wasn't turned to "cold"? When/if the soundstage is 10 degrees cooler than the green room, the pre-entrance tuning can be moot. Been there done that.

From Wikipedia:

Musical talent
Gleeson is a fiddle and mandolin player, with an interest in Irish folklore.[3] He played the fiddle during his roles in Cold Mountain, Michael Collins and The Grand Seduction, and also features on Altan's 2009 live album.[15] In the Coen brothers' The Ballad of Buster Scruggs (2018), Gleeson sings "The Unfortunate Rake". He has also made a contribution in 2019 to the album by Irish folk group Dervish with a version of Rocky Road To Dublin.

[Dagger Gordon]

Brendan is a pretty good musician - no question.
I have a Mary Staunton CD which he plays on called Circle Of Friends (2010) where Mary notes that she has known and played with Brendan for over 20 years.
In fact he plays not only fiddle on it but also guitar. I haven't heard it for a bit, but I remember the guitarist playing the tune on one track and checked out who was doing it, and then realised it must be him.

I used to have a Gibson from the teens a bit like Brendan plays and I have to say I never really gelled with it, so I sold it and got a Collings MT which I've been much happier with.

They're not for everyone. But few would deny that Marla Fibish makes hers sound great, for example.
Another person who gets a great sound is Robin Bullock. Check out out his Mandolin Mondays performance from 2019 on his 1920 Gibson. Altered tuning. Pretty fantastic, actually.

https://www.youtube.com/watch?v=kc7H25hCyYk