Companion of Krishna in superhuman feats
Keshava wrought the feats 'together with Rama': 'saha ramena' (SB 1.1.20).
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Balarama
बलराम
Also known as राम · Rama (Balarama)
Balarama is Krishna's elder brother: son of Vasudeva and Rohini, the mighty Yadava, bearing the plough (Halayudha) and identified in tradition with Sankarshana; he is Krishna's constant companion in every pastime. In the processed verses: 'krtavan kila viryani saha ramena kesavah' — Keshava wrought superhuman feats 'together with Rama' (SB 1.1.20; Rama = Balarama, unanimous reading). Of the 'rama-krishnau' pair born in the Vrishni clan (1.3.23), he is counted among the Lord's portions by SB 1.3.28's summary.
Śrīmad Bhāgavata Mahāpurāṇa 1.1.20 — Sanskrit Wikisource (pinned oldid=110172)
Balarama — born in — Vrishnis
Balarama (the 'Rama' of the rama-krishnau pair) obtained birth among the Vrishnis: 'vrsnisu prapya janmani' (SB 1.3.23). Evidence: EXPLICIT.
Balarama — avatara of — Krishna
Balarama is counted among the Lord's portions: the pair 'rama-krishnau' (SB 1.3.23) plus 'ete camsa-kalah pumsah' (SB 1.3.28). Evidence: EXPLICIT (via the summary verse).