autonomous; self-directed; proactive
Describes acting on one's own initiative, without external control. Often used in contrast to 受動的 (passive).
He proactively advanced the project.
A proactive attitude is required, not a passive one.
自主的 also means autonomous or voluntary, but often stresses independence from outside influence or self-governance. 主動的 focuses more on taking the lead or being proactive in a situation.
Compound of 主動 (shudō, 'initiative, taking the lead') + 的 (-teki, '-like, -ive'). The exact historical derivation is uncertain, but the word follows a common pattern for forming adjectival nouns from Sino-Japanese compounds.