Smaug vs the Sutherland Red Dragon

Left: Smaug by Tim Kirk (1975). Right: the cover of the Holmes Basic Set (July 1977). 
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David Sutherland painted a cover for the Holmes Basic Set that remains one of the most iconic early D&D illustrations. It literalized the title of Dungeons & Dragons, showing a dragon in a dungeon. The viewpoint is as if we are members of the party of adventurers who have just entered the chamber and disturbed the huge red dragon resting on its seemingly endless bed of gold and treasures.

This image has influenced the cover art of many successor sets ranging from later TSR D&D Basic Sets to the Pathfinder Beginner Box. Sutherland's take on the Red Dragon appeared in other D&D products of the era, including the Monster Manual and Monster Cards.

The 1975 Tolkien Calendar

Sutherland's dragon was in turn possibly influenced by an earlier image of red dragon on a pile of gold that was published about two years before Holmes Basic. This was a stunning depiction of Smaug by Tim Kirk that appeared in the 1975 Tolkien Calendar, which included works done as part of his MFA from Cal State. In particular, note the similar (but not identical) poses of the dragons, the head "whiskers" of the dragons, and the wide ventral neck scales. There are also similarities in the treasures embedded in the pile of gold, including urns, chests and embedded swords. There's even an arching shape over the head of each Dragon (vaulted ceiling for Smaug, entrance archway for the Sutherland Dragon).

Source: The Complete Guide to Tolkien Calendars

Kirk's illustration in turn appears to be a modernization of Tolkien's own "Conversations with Smaug", which appears in the Hobbit itself. Note how Tolkien has placed skulls on the floor around the pile of gold and compare this with the skulls in Kirk's pile of gold:

Source: The One Ring

Additional Evidence: Pig-Faced Orcs

By the mid-70s, Tolkien's Middle-Earth books had grown extremely popular and the 1975 calendar was the first to feature art from an artist other than Tolkien himself. It's easy to imagine that a fantasy artist such as Sutherland would have encountered this calendar. But there is one other bit of evidence that Sutherland was familiar with the Tolkien Calendars. The 1976 Tolkien Calendar (which would have been published in mid-to-late 1975) included art by the Brothers Hildebrandt, including this image of very pig-faced orcs: 

And Sutherland was the one who slightly thereafter introduced pig-faced orcs into D&D, via his illustrations in Swords & Spells (July 1976, per the Acaeum), Holmes Basic & the AD&D Monster Manual.

This illustration is spread across two pages in Swords & Spells. 
Source: OldSchoolFRP

See also:

David Sutherland Day