What's a word for someone whose personality or character changes a lot and get more affected than others by other's company or influential people? [duplicate]

Solution 1:

I prefer impressionable, as suggested by @KarimTabet, but I will add gullible and credulous to the possibilities he suggested. From Lexico:

gullible: Easily persuaded to believe something; credulous.

credulous: Having or showing too great a readiness to believe things.

"Someone whose personality or character changes a lot and get [sic] more affected than others by company or influential people" is more impressionable, gullible**, or credulous** than others.

Solution 2:

The person's personality would be described as malleable:

[Merriam-Webster]
2 a : capable of being altered or controlled by outside forces or influences

Using it with the example sentence:

He is a malleable type of person.

Or, more naturally:

He is weak-willed, and has a malleable personality that is easily influenced and changed by others.

Solution 3:

It doesn't fit your sentence well, but the person could be considered a chameleon (M/W def 2)

a person who often changes his or her beliefs or behavior in order to please others or to succeed

By analogy to an actual chameleon, which changes coloration to match its surroundings.