Mighty and Mac are a double-ended Fairlie duplex locomotive, and conjoined twins. Mighty is the "older" of the two and is distinguished by a small flick of hair. Mac is the "younger" half and is distinguished by his youthful features, round nose and freckled cheeks.
Despite the opposing personalities of the two ends, they are technically one engine.
Thomas and Friends
Prior to their adoption into the Skarloey Railway family, Mighty Mac had only worked in the shunting yards. Their lack of knowledge beyond their boundaries created much conflict between the two halves (for example, which end is in charge of doing what) when they pulled their first train, which placed themselves and their passengers in great danger whilst running an important errand. But, with advice from Thomas in mind, they were able to complete their task and realise the value of working as one.
Mighty Mac is two engines in one. He is Mighty on one end and Mac on the other-- making him one of the most unusual engines working on the Skarloey Railway. When Mighty and Mac work together, Mighty Mac is the strongest engine on the Railway. But when they don’t, Mighty and Mac pull each other backwards and forwards, only to end up right where they began.
Mighty Mac is based on a Double Fairlie locomotive of the Ffestiniog Railway with added buffer beams. A Double Fairlie locomotive from the same railway appeared in the 1979 Annual. Three of these are currently in service on the Ffestiniog - another is preserved at the National Railway Museum, and another is under construction at Boston Lodge.
Mighty and Mac are painted royal blue with yellow and red lining. On Mighty's side, his cab windows and tank caps are lined with yellow, while on Mac's side, they are lined with red.
- Season 9 - Mighty Mac, Tuneful Toots (cameo), Rheneas and the Dinosaur (cameo), The Magic Lamp (cameo), Duncan and the Old Mine (cameo) and Skarloey the Brave (cameo)
- Season 10 - A Smooth Ride (do not speak), Duncan Drops a Clanger, Thomas' Tricky Tree (do not speak), Which Way Now? (cameo), Duncan's Bluff (stock footage cameo) and Missing Trucks (do not speak)
- Season 11 - Sir Handel in Charge, Cool Truckings (cameo), Ding-a-Ling and Wash Behind Your Buffers (cameo)
- Season 12 - Mountain Marvel (Mac; does not speak) and The Party Surprise (cameo)
- 2008 - The Great Discovery
- Season 10 - Navigation, There's Always Something New, Responsibility, Strength and Jingle Bells
- Season 11 - The Narrow Gauge Engines
- The Great Discovery - Where, oh Where is Thomas? and Thomas, You're the Leader
- Season 10 - Sodor's Special Places - Narrow Gauge Railway (do not speak)
- 2006 - Mighty Mac
- 2009 - Sir Handel is the Manager and Trainloads of Fun
- 2011 - The Big Book of Engines and Mighty Mac the Double Engine
- 2012 - Do Not Quarrel! Be Lost and Full Steam Ahead!
- 2015 - Mighty and Mac Work it Out
- 2006 - Pull Together and Pulling Together
- 2008 - Smokescreen
- 2009 - The Party Surprise!
- 2010 - Going First
- 2008 - Begins Educational Learning
- 2017 - Read and Play!
- Mighty is the only engine to have what appears to be hair (excluding facial hair).
- Mighty Mac has used two whistle sounds in the television series. Also, they have a whistle at both ends of their model unlike most Double Fairlies.
- Mighty’s original whistle sound was later used for Bert.
- Mac's original whistle sound was later used for Rex.
- Out of all the characters introduced in the ninth and tenth seasons, Mighty Mac is the only one to not be mentioned in the song, "There's Always Something New."
- In the German dub since the tenth season, Mighty Mac has been called Big Mac, which is also the name of a TUGS character.
- Mighty Mac's whistle sound was used for Thomas in the Robot Chicken episode "Ext. Forest - Day".
- Mighty's Hair changes position depending on what emotion he's expressing.
- Wooden Railway (normal and cancelled Talking Railway Series version; discontinued)
- Take Along (discontinued)
- Take-n-Play (discontinued)
- Motor Road and Rail (discontinued)
- TrackMaster (discontinued)
- My Thomas Story Library (discontinued)
- Capsule Plarail (normal and metallic)