Strength is a many faceted thing. You can encounter it physically, mentally, emotionally, and there is strength of patience, of the moral variety. Strength can be found in the good, and in those who have maybe not the best of intentions as well. It is a thing which can be literal - physically personified - and just as easily a thing of depth, hidden but just as voluminous. It can be found in men as well as women, and as these texts show, in aliens and theory too. 

In this image I see the people of Uruk. For years, decades even, they were strong in the face of Gilgamesh's abuse (tablet I lines 163-173)
This represents almost a literal image of Gilgamesh and his described perfection and strength (physically). (tablet I 156-162)
The journey and meeting of Gilgamesh/Enkidu with Humbaba. They only wanted to kill him once they knew they had the combined support - much like these bullfighters facing a wild bull (tablet Y 100-115)
People escaping civilization. One of the ways to be strong, avoid displeasure and unpleasure (Freud 45), is to isolate yourself from civilization.
"I cannot think of any strong as the need for a father's protection" (36); Freud is known for his theories of sex, so those who give up the flesh exhibit a sort of strength
Man found a reason for keeping his sexual object near, and woman found safety/comfort in having the stronger male around to protect her young (Freud 78). Family, made two otherwise unhappy/searching - weak - individuals, strong
Therem, at his end (Le Guin 305). His strength - both of character and mentally, his perseverance on the Ice as well as persistence in furthering Genly's cause - was strength
Argaven, tired, worn - maybe dejected, meeting with Genly for the second time. The strength here appears in Argaven. Putting aside his fears and lunacy to do what's best for the planet(314)
Without Therems' strength and knowledge to guide him, Genly would have died long before escaping prison. This is the two of them, on the Ice, crossing it - pulling the sledge together so to speak. (258)
Similarly, beginning of the Ice. Drumner and Dremegole; the mouth of their journey across the Ice. This difficult time, of trials and tribulations, not only tested the two physically but mentally as well.(241-248)
A metaphor of Socrates; his vigor of mind and relentless prodding of those he finds interesting (13). It takes a certain strength of character/perseverance, to question others as thoroughly as Socrates likes to.
Socrates being questioned by Crito (43). The strength lies in denying life, the easy way out - fleeing. Instead he stays and does the noble thing, accepts his punishment.
Mrs. Cheveley disclosing the letter to Sir Robert (15). She had to have some kind of strength to be so bold and brave, as a woman blackmailing a politician, in that time.
Lord Goring used the brooch/bracelet that Mrs. Cheveley stole as leverage (59) to get her to drop the blackmail with Sir Robert. A brave (thus strong) move when you consider how ruthless she is.
"the greatest carving" (Daodejing 28). Nature, here actual grass/shrubs, grown over stone or metal - nature and manmade in harmony. Lines blurred, working peacefully, inconspicuously. The essence of the Dao
There is no greater wrong than to prepare to defend yourself (Daodejing 46). Having the strength to know you need to defend yourself, but not acting on it. Especially when you are a soldier.