Go forth and …

• Since the currently highest voted answer seems to be wrong (even though it seems to fit perfectly!), can you please provide a hint to point us to the correct (as in, intended by you) direction? – Christoph Feb 19 '18 at 10:50

Robert Wadlow, who wore US size 37AA (UK 36) shoes. (For a single word answer, then I suppose just "Wadlow".)

Reference: http://www.guinnessworldrecords.com/world-records/largest-feet-ever

Reasoning:

When you multiply the numbers on the calculators together the product is $3215.3045$. Turn that upside-down on a calculator display like those in the picture and it reads SHOE.SIZE.

• Creative! But not the solution – user45515 Feb 17 '18 at 12:25
• Nice one. Also, "Wadlow" sounds like wallow, which appears to be what the calculators are doing in the water. Edit: Ah, damn, just seen OP's comment above mine. – Phylyp Feb 17 '18 at 12:25
• @user45515 You mean ... that product is a complete coincidence ?! – Rubio Feb 17 '18 at 12:26
• Yep! I think that was actually a pretty amazing coincidence. – user45515 Feb 17 '18 at 12:29
• The title is kind of proving it too. Is this also a coincidence? – ibrahim mahrir Feb 17 '18 at 17:02

3.402823 × 10^38 ?

Because the picture shows

floating calculators.

So the "greatest of all"

is the largest single-precision floating-point number in the IEEE standard.

I think the answer is :

50238

Because:

When read upside down on a calculator, this spells "Bezos", the man with the greatest fortune and the owner of Amazon (the Amazon river is pictured as far as I can tell). I believe the "Go Forth and..." quote is a red herring to imply multiplication. It could be read as "Go Forth and Prosper," which Bezos has done, no doubt. Although, I am suspicious that the "who had" question could imply a dead person...

• But how does it explain the 4 calculators and the numbers displayed? Fine, 7.33 can be read as eel, and the Amazon river has electric eels, but what about the other numbers? – Phylyp Feb 18 '18 at 2:29
• Unfortunately not the solution. – user45515 Feb 18 '18 at 3:26

2.83, its floating higher in the water than the rest

• welcome to Puzzling SE. I've added a spoiler to your text to avoid revealing it inadvertently. Do take a look at the tour page to familiarize yourself with the Puzzling community. – Phylyp Feb 18 '18 at 13:02
• This is also not correct – user45515 Feb 18 '18 at 13:16

Turning the whole thing upside down makes the calculators' displays read:

EEL EBZ IE S

No idea what that means. According to Google

The largest shoe measures 18 ft 0.53 in x 6 ft 11.07 in and is 9 ft 6.17 high

and it has a

Converse

logo on it.

• Nope :) Interesting though – user45515 Feb 18 '18 at 8:40