Probably Hexanerax 2 in Childhood's End by Arthur C Clarke, given that Robert L Forwards's Dragon's Egg is a neutron star not a planet.
Here's how it is described: The planet was absolutely flat.
Its enormous gravity had long ago crushed into one uniform level the mountains of its fiery youth--mountains whose mightiest peaks had never exceeded a few metres in height.
Yet there was life here, for the surface was covered with a myriad geometrical patterns that crawled and moved and changed their colour.
It was a world of two dimensions, inhabited by beings who could be no more than a fraction of a centimetre in thickness.
That's pretty much all we know about it -- it's a throwaway vision, not the setting for any of the novel.
(Hal Clement's Mesklin from Mission of Gravity is an obvious contender, but its gravity is a mere 3G at the equator where the known life is, and 665G at the poles, which is probably still less than Hexanerax 2 as described.)
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I'll venture that the winner is none other than our old favourite; Krypton .
Without focusing on specific numbers, the surface gravity on Krypton would have to be tens of thousands of times heavier than Earth to meet the description below.
It was "The Black-Hole Planet."
Nothing ever left.
It was as dense as a newborn star and as dark as the pit.
From a more conventional planet with crusted frozen oceans, life should at the very least have reflected so much that astronomers in nearby systems might at first have mistaken it for a star.
It was so heavy that space itself contracted around it.
A dull green glow, the backwash of starlight that collected in its atmosphere, reflected downward to streak Krypton's daytime sky with red-shifted luminous clouds and light its nights with a phosphorescent pink.
The light radiated from every horizon.
The days were barely brighter than Krypton's nights.
It took an enormous expense of energy to launch anything from the world's surface.
Even a nuclear-powered vessel designed to accelerate across lightyears of space needed to tap the thermal energy of the planet's underground in order to trigger a reaction big enough just to escape Krypton's terrible attraction.
Even on a world whose population's profligate use of energy had actually slowed the planet's self-destruction, Jor-El realized that his use of so much power in one burst would certainly attract attention.
He gave himself the chance to make the only test of his prototype starcraft.
If we're just looking at heavyworld sci-fi in general, then you can't got far wrong with Flux by Stephen Baxter.
The main characters are tiny humans living inside the surface of a neutron star rather than merely living on the surface, like the wimpy lifeforms in Dragon's Egg
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I don't remember the name of the story; but you didn't ask that.
I believe that the answer might be Jupiter .
Isaac Asimov wrote a short story in his robots series about the "ZZ" line of robot,which was designed to travel to the surface (!) of Jupiter.
Three of them traveled there in a non-airtight spaceship(rather than try to build something that could withstand the atmospheric pressure).
They encountered creatures that were sufficiently
advancedthat they attacked the robots with weapons (although not effectively).
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By far not the one with the highest density (looking at Mike's and Richard's answers here), but Perry Rhodan issue #16, "Die Geister von Gol", was about a planet of 916g surface gravity, making it a #3 entry at the time of posting.
;-)
Rhodan and his crew navigated the surface with tracked multi-purpose vehicles ("Shifts"), which needed their anti-gravs (usually used to let them fly) running at max output just to keep them mobile (and not crushing the crew).
I am not sure if you could call the beings they encountered "life forms" (and neither were the protagonists), as they seemed to be energy-beings, but they were attracted by the vehicle's shields (reacting to stimulus), and drained their power supply, growing in size in the process (feeding, growth), so let's call them "life".
The highest gravity planet to bear human life in the PR universe would be Oxtorne, a 4.8g world.
A shipwrecked crew of emigrants managed, with the help of genetic engineering, to adapt to the harsh environment of their world within four generations.
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Not as much gravity as a neutron star, but Iain M Banks's The Algebraist features a race called the Dwellers who float around inside of gas giants throughout the galaxy.
ZanLynx mentioned in the comments the Hades Matrix from Alastair Reynolds's Revelation Space series, a neutron star that was somehow converted into an impossibly dense and powerful computer so that a long-dead race could go on living as programs within the matrix.
So they're not exactly life forms in high gravity, but maybe it still counts.
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First Mesklin popped my mind from "Starlight" by Hal Clement.
It is a true planet (not a neutron star like Hexanerax2) and it has a solid surface (unlike the aforementioned gas giants), but it has a size of a smaller gas planet and a shape
so distorted that the strenght of the gravity on its equator is slightly different than on its poles.
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Stephen Baxters Flux tells a story about a "human" civilization living on a neutron star.
Not really humans, but made by humans to be able to live on the neutron star.
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I've just started reading  Foundation  and Gaal Dornick has landed on Trantor for the first time and notices that:   The air seemed thicker here, the gravity a bit greater, than on hishome planet of Synnax...   This prompted me to wonder,  what is the highest gravity planet mentioned in science fiction that has lifeforms?  Edit 1: I am specifically asking about planets with solid surfaces.  Edit 2: I am referring to the gravitational force at the surface.
In science fiction, which planet with lifeforms has the largest gravitational force?
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<hard-sci-fi><gravity>
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Hexanerax 2, Krypton, the planet in Flux by Stephen Baxter, and Oxtorne are all suggested answers to this question. The possibilities are as follows: Hexanerax 2, Mesklin, Krypton, the Black-Hole Planet, Jupiter and Oxtorne. The planet in Flux by Stephen Baxter is also a contender.
The possibilities are as follows: Hexanerax 2, Mesklin, Krypton, the Black-Hole Planet, Jupiter and Oxtorne. The planet in Flux by Stephen Baxter is also a contender.