When i bought my GBA in 2001, Pokemon Silver was my first Pokemon game, i've only played on emulators before because i didn't have a GB or a GBC...
When i found Entei, i got fissured into caching one, and it took me three days to do it, since i had no Master Ball, i caught him with my bara hands... I will never forget these good times... Entei is really one of my favorite Pokemon...
In Pokemon Colosseum i was scared of losing the battles, i felt way too much pressure, until i finally found Entei, and when i caught him, the game got easier for me, the fear was gone.
I always thought "If anything ever happens i send Entei out" uhhuhah...
By the way my level 100 Entei is the one from Pokemon Colosseum. I have many more Enteis in other games, but i still use that one.

By the way, in that time i had a dream, but it was more like a nightmare...
*dream*
I was walking on a cave-like place, it was dark, and i was alone. I walked more and more until i found an exit. When i left that place, i say a canyon and i could see the end and the ground was dry and i continued walking, until, suddenly, i found Entei. Wow! I breathed heavily, and i talked with him
-"Entei, are you here?!?"
And he said:
-"It's alright now"
*/dream*

I was like 23 that time, but that Pokemon was always a body guard for me. When i go through a problem, i think "I'll be as strong as Entei". The third movie is my favorite just because of Entei.

Anyway, Entei is a president for me.