The Idolator was created by the corrupt Warp Smiths and Dark Mechanicus cohort accompanying the war bands. The Thunderer tanks found mothballed in vast underground storage facilities were far to slow and heavy to keep up with the other chaos space marine elements, and so the multi-fuel engines were upgraded, and improved filtration systems were added to cope with the toxic particle-choked atmosphere. Armoured blades were attached to the front, and the hull was raised to allow space marines to get inside and man the tank. Some daemons were even transferred into the tanks to replace them; in cases where their previous vehicular prisons were unrepairable, but intact enough to prevent the daemon escaping.
Whilst not as efficient as the Vindicator, the Idolator is an effective enough substitute, and the fleet of chaotic war-machines helped turn the tide of the war, and bring another valued planet to the forces of chaos. Many remain in service with the war-bands. After decades of testing and research, the Idolator MKII was found amongst dozens of chaos warbands in mid-M39. Fitted with armour plating commonly seen on Astartes tanks, it was much lighter and more resistant to spalling than conventional Imperial armour. Many examples mounted far more elaborate weaponry, such as Laser Destroyers, making them incredibly deadly hunter-killers. Thse MkIIs are, for now, fairly rare, but as more Heteteks research forbidden works, production is likely to develop even further.
A few years ago, I made the Idolator: a stand-in for Vindicators, using an old Leman Russ that wasn't getting any action on the table-top. Now I find myself back again with the chassis, and I have started work on two, more detailed versions of this original tank.
The main difference at this early stage is adding new armour plating, more in-line with other Astartes vehicle. The new profile of the tanks suggests it is a 'missing link' tank, much like the Sicaran, between the Rhino and the Land Raider. 
I had been toying with using them as normal Vindicators or even Rhinos, but I've decided to make the vehicles Vindicators, with swappable main guns. Laser Destroyers are first on the list, as they're great for punching through armour (which the army in it's current form struggles with). Six twin linked ordinance AP1 Lascannon shots from two of these monsters is sure to break through even the toughest plating.
The plan is to make the main guns removable, with guns simply slotting into the gap in the front. Armour panels will help hide the gap and integrate the weapons systems.
Once the hull had been blocked out, I'll work on getting the body detailed with additional armour and systems, before finally getting the guns ready.